The Effect of the Project-Based Learning Approach on the Academic Achievements of the Students in Science Classes in Turkey: A Meta-Analysis Study

Abstract

Keywords In this research, the study of the meta-analysis is conducted to identify that the project-based learning approach affects the academic achievements of the students in science classes. Therefore, related literature of studies done in Turkey is reviewed. Master, doctoral dissertations and articles (between 2002 and 2013), related to the research problem and having statistical data about the study of the meta-analysis, are analysed by scanning from national and international database in Turkish and English. There are 41 studies including the sample about the effects of the project-based learning on the academic achievements of the students in science classes. 42 effect size values were obtained from these studies. The result of the meta-analysis shows that the project-based learning approach is more effective than traditional teaching methods about the academic achievements of the students in science classes. The effect size of the Project-based learning approach, between 0,777-1,218 confidence interval, has been found 0,997 (%95 CI, SE=0,112) about the academic achievements of the students in science classes by using random effect model. This value is moderate level to Cohen, Manion and Morrison's the classification of the effect size (2007). Among the studies that are included in this study, 39 of 42 studies have positive, 3 of 42 studies have negative effect size value. Intermediate variables (moderator) analyses have been done at meta analysis studies, natural sciences, education levels, sample size, application time, used methods and types of publications. In these studies that have positive effect value; three of them are at poor, five of them are at modest, eleven of them are at moderate and twenty of them are at strong effect size level. As a result of analysis done by the intermediate variables the highest effect sizes have been observed at high school degree (ES=1,536), in physics (ES=1,046) and between 1-20 lesson hours (ES=1,203). The highest effect size in all variables has been observed at high school degree (ES=1,536). At the end of the study; according to the results of the research, there are some recommendations for the researchers and instructors. Academic Achievement

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Education and Science
Vol 40 (2015) No 178 255-283
255
The Effect of the Project-Based Learning Approach on the Academic
Achievements of the Students in Science Classes in Turkey: A Meta-
Analysis Study *
Mehmet Fatih Ayaz 1, Mikail Söylemez 2
Abstract
Keywords
In this research, the study of the meta-analysis is conducted to identify
that the project-based learning approach affects the academic
achievements of the students in science classes. Therefore, related
literature of studies done in Turkey is reviewed. Master, doctoral
dissertations and articles (between 2002 and 2013), related to the research
problem and having statistical data about the study of the meta-analysis,
are analysed by scanning from national and international database in
Turkish and English. There are 41 studies including the sample about the
effects of the project-based learning on the academic achievements of the
students in science classes. 42 effect size values were obtained from these
studies. The result of the meta-analysis shows that the project-based
learning approach is more effective than traditional teaching methods
about the academic achievements of the students in science classes. The
effect size of the Project-based learning approach, between 0,777-1,218
confidence interval, has been found 0,997 (%95 CI, SE=0,112) about the
academic achievements of the students in science classes by using
random effect model. This value is moderate level to Cohen, Manion and
Morrison’s the classification of the effect size (2007). Among the studies
that are included in this study, 39 of 42 studies have positive, 3 of 42
studies have negative effect size value. Intermediate variables
(moderator) analyses have been done at meta analysis studies, natural
sciences, education levels, sample size, application time, used methods
and types of publications. In these studies that have positive effect value;
three of them are at poor, five of them are at modest, eleven of them are
at moderate and twenty of them are at strong effect size level. As a result
of analysis done by the intermediate variables the highest effect sizes
have been observed at high school degree (ES=1,536), in physics
(ES=1,046) and between 1-20 lesson hours (ES=1,203). The highest effect
size in all variables has been observed at high school degree (ES=1,536).
At the end of the study; according to the results of the research, there are
some recommendations for the researchers and instructors.
Academic Achievement
Science Education
Meta-analysis
Project-based Learning
Effect Size
Article Info
Received: 10.02.2014
Accepted: 04.15.2015
Online Published: 05.04.2015
DOI: 10.15390/EB.2015.4000
* This study was produced from Mehmet Fatih Ayaz for the doctoral thesis that prepared under the supervision of Assoc. Dr.
Mikail Söylemez
1
Dicle University, Ziya Gökalp Faculty of Education, Department of Educational Sciences, Turkey, mf_ayaz@hotmail.com
2
Dicle University, Ziya Gökalp Faculty of Education, Department of Educational Sciences, Turkey,
soylemezmikail@hotmail.com

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Introduction
In the modern information age, there is big information burst in science and they are all the
consequences of technology. Although easier to get information, even scientists have difficulties in
keeping track of developments and changes in current information age (Tan & Temiz, 2003). The
necessities of 21st century for humanity are to develop and change in accordance with science and
technology which prospers everyday. To address these needs, there is a need for individuals who
have more information and skills which will quide them to access to information. Especially, there is
an urgent need for the individuals who know how to get this information. Direct transfer of
information, beliefs, and feelings of the individuals are not sufficent and effective to turn the societies
into the modern one.
Developments in science and technology are the driving force behind the fast changes in the
social, political, economical, and cultural systems (Ünal, 2005). Therefore, individuals who are the
basic source of social development need to be trained in order to meet changable needs and
expectations. The first absolute necessity emerged due to the science and technology which is
improving fastly is to take our scientific manpower to the universal level and make ensure to advance
as an information society. The only way of making use of science and technology, the main source of
comfortable and free-living, is to be an individual who can effectively use them. The one of the most
effective ways of achieving this is education (Soylu, 2004).
Forming a modern structure in education can be accomplished through the training of the
researchers (Gökmen, 2003). Today, the individual competencies expected today are to access to
information, evaluate the information, to use the information in an effective way, and to transform
these acquired information into skills (Erdem and Akkoyunlu, 2002). Starting from primary school to
university, in the solution of problems, scientific method should be followed, and through education
individuals need be supported to form it as a habit. Creating new information entailed by the change,
educational institutions should contribute to this change and the training of individuals who can think
critically (Gürol, 1995). Until today many education models have been exploited with various methods
and techniques. The oldest and the most used one among these methods is traditional method which
is a plain lecturing. Besides, question-answer, discussion methods can be also seen as traditional
teaching methods, since alone they can no longer be accepted as contemporary methods. Today,
lecture, question-answer, and discussion techniques alone do not seem very easy to gain the aimed
skills to the individuals. In today's modern educational approaches, it is aimed to nurture individuals
who have high logical thinking competence, can interrogate and search the information, cope with the
problems, and learn to learn (Demirel, 2012).
For this reason, ‘constuctivism’ word has been started to used noteworthily in educational
research and discussions (Cunningham & Duffy, 1996; Kinnucan-Welsch & Jenlink, 1998). Discussion,
activities for the interests and needs of learners, a certain state of uncertainty to provide creative
thinking and colloborative works take place at constructivist learning environment (Taylor, Fraser &
Fisher, 1997). Students are activated and guidanced for solving problem by cooperative studies in
such environment. It is benefited from experiences of students during this studies (Rice & Wilson,
1999). Individual solve problems based on his past experiences and configureted informations
benefiting from multiple sources (Maypole & Davies, 2001). Although this approach learner-focused,
it gives teachers important tasks since information isn’t transferred directly to students and teachers
lead students only to access to information (Bryant, Kastrup, Udo, Hislop, Shefner & Mallow, 2013). It
is observed that constructivist learning approach used in almost every field is used more frequently
and effectively in some areas.
Considering these characteristic features expected by our modern age, science (science and
technology, physics, chemistry and biology) education comes into prominence. Development in
science and technology are parallel to the one in physics, chemistry and biology. One of the most
important features need to be gained by students through science is scientific method skills. The

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attempts to gain these skills with the use of traditional methods such as lecture may not provide
effective results. Project-based learning is one the teaching method in parallel with constructivist
learning approach to realize this goal.
The project based learning has a long history. John Dewey’s Reconstructivism and Active
Learning Model, Kilpatrik’s Project Method, Bruner’s Discovery Learning can be said as foundation
stones of PBL (Korkmaz ve Kaptan, 2001). PBL was discussed for the first time in Kilpatrick’s article
named “Project Method”. At first the method was developed to solve the problems faced in real life by
using several educational techniques (Korkmaz, 2002). However, the real founder of the method is
John Dewey (Dewey, 1997). The Project method is based on Dewey’s active learning theory. On the
basis of The Project method, considered as one of the applications of American public education
system, lays Dewey’s new school life and students’ learning how to solve the problems by themselves
(Dewey, 2013). The most important names who synthesized Dewey’s studies and took it a step further
were his students “Kilpatrick and Collins” (Çubukçu, 2011).
In general, project based learning is defined as students’ individual and group works in long
period to reach a concrete product. The main goals of project studies are to help students to take
responsibility for their education, to develop their positive risk taking behaviour, to motivate them to
cooperate with others (Bilen, 2002; Korkmaz & Kaptan, 2002; Saban, 2000). With project based learning
approach, we aim to gain students scientific skills and parallel to that to increase students’ academic
achievement.
Problem
So far the number of scientific studies has increased rapidly. Different results may be drawn in
different studies which were independently done on one particular subject. It may be reached
different results in made in a particular subject, independent studies. Even studies are planed to have
overall generalizations; they can not give overall explanations due to their limitations related to
sample size, time, transportation, the number of practitioners etc. Researches are generally done
without being related to other studies and concluded with the fact that further studies should be done
(Özcan, 2008).
Because of the nature of social sciences, incidences and phenomenon are examined in their
environment. Researcher tries to explain and intrepret these in their environment (Yıldırım & Şimşek,
2011). Based on the researches in social sciences, it can be seen that further study attempts are not kept
on till more concrete solutions to the problems are taken (Karasar, 2005). There is need for more
comprehensive and reliable studies to interpret the accumulated information in social sciences and to
conduct new studies (Akgöz, Ercan & Kan, 2004). If we describe the science as collecting and
commenting on this information, it is very important for the investigation, the review and synthesis of
the study which deals with the same research problem to be valid and reliable. The system applied in
meta-analysis includes quantitative analysis and synthesis of the studies in research literature
(Chambers, 2004; Wolf, 1986). It combines the results of the study in a coherent and consistent manner
(Cohen and Manion, 2001).
Although meta-analysis starts to be a very popular method in recent years, in 1904 it was
Pearson who was the first doing quantitative analysis of the findings obtained from the studies on five
different samples that set out the relationship between the vaccinated and the death. Since the year
1930, it has been a seriously studied method. In 1932, Fisher developed a method that combined the
results of different experiments. In 1954, Cochran used a method of analysis that enabled the
comparison of different studies carried out at different times and in different places (Sarıer, 2013). In
the 1970s, Glass was the first scientist to use the name of meta-analysis in behavioral and social
sciences, combining quantitative effect sizes found from studies in experimental and control groups
(Shelby & Vaske, 2008). In 1976 the process, which was developed by Glass and made a combination
of 375 results of the psychotherapy studies, was called as "meta-analysis" (Lipsey & Wilson, 2001;
Üstün & Eryılmaz, 2014; Şahin, 1999). In the 1980s, the meta-analysis was developed by the addition of

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new statistical methods (Cooper, 2010). Glass (1981) and Hunter published Schmidt and Jackson’s
(1982) book containing meta-analysis methods (Akçil & Karaağaoğlu, 2001). In the 1980s, thanks to the
commitment of Peto and colleagues at Oxford, meta-analysis developed very much. Hedges and
Olkin (1985), and Petitti (1994) in detail describe the meta-analysis statistical methods; Greenland
(1987), on the other hand, identifies the statistical methods for the meta-analysis of non-experimental
studies (Çağatay, 1994).
Big studies fed from the literature reviews benefit from lots of studies to make general
descriptions (Cooper, 2010). This thought is the main goal of literature reviews and meta-analysis. Big
studies provide the politicians of education and researchers with the opportunity of which is formed
by the synthesis of the individual studies and which shows the “big picture” and supplies scientific
generalization. To be applied practically, social and treatment science need for data which is practical,
brief, proved quantively in terms of its effect, and can be core for the new studies (Özcan, 2008).
The educational programs in Turkey were reformed in 2005 by taking the constructivist
learning approach to the centre. In addition to this, the importance of Project Based Learning (PBL)
approach has increased and this importance has been put fprward in many researches. In Turkey and
in the world, there are many studies on the subject of “Project Based Learning Approach” (Altun,
2008; Baran, 2011; Barak & Dori, 2005; Benzer, 2010; Chang, Wu, Kuo & You, 2012; Demir, 2008;
Doppelt, 2003; Frank & Barzilai, 2004; Girgin, 2009; Hun, Hwang & Huang, 2012; Kaldi, Filippatou &
Govaris, 2011; Korkmaz, 2002; Mioduser & Betzer, 2007). Generally these studies explored the effect of
PBL approach to the academic achivement (Baran, 2011; Güven, 2011; İmer, 2008; Keser, 2008; Köse,
2010; Tuncer, 2007), attitude (Baran, 2007; Benzer, 2010; Deniş Çeliker, 2012; Keser, 2008; Koçak, 2008;
Serttürk, 2008), science process skills (Acar, 2011; Gültekin, 2009; Özahioğlu, 2012; Yurdatapan et al.,
2013; Zeren Özer, 2011), motivation (Aslan, 2009; Keskin, 2011), critical thinking (Korkmaz, 2002) etc.
In some of the studies there are significant differences between the effects of PBL approach and
traditional teaching methods (Doğay, 2010; Girgin, 2009; Güven, 2011; Özcan, 2007; Serttürk, 2008);
however, there is no significant difference in others (Avcı, 2006; Değirmenci, 2011; Gültekin, 2009;
Tuncer, 2007). Researches which are done based on the different perspectives about PBL approach
need to be combined, synthesed, and evaluated.
Nowadays there are few subjects which are not related to science. Many issues like
environment, societal health, the production of tools to make life easy and protect society are all
concerned with science. Therefore, to gain all individuals the skills needed to some extent to
understand the basic subjects which the society is faced and to apply them can be accepted as the main
goal of science (Howe, 2002).
Especially in spite of a great number of studies about the effects of PBL approach on the
academic achievement in science classes, there is not any meta-analysis study during the search.
Demiray (2013) and Kaşarcı (2013), have beendone meta analysis study by the effectiveness of PBL
approach. However Demiray (2013), has made studies on the overall impact of the PBL approach.
However Kaşarcı (2013) have examine the effectiveness of PBL approach to science lessons since
primary studies are less than this meta-analysis study and he didn’t analyse intermediate variables, so
these studies are different from purpose of this meta-analysis study. In this respect, there is an
importance to find answer to the question of “What is the possible effect of project-based learning
approach to the students' academic achievement in science classes?”

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Purpose
The purpose of this research is to identify the students’ academic achievements in science
classes (Science and Technology, Physics, Chemistry, Biology) through the use of meta-analysis
methods comparing the methods of PBL approach with traditional education. For that reason, the
meta-analysis of the studies found in the literature has been carried out. In addition to this, various
characteristics which are thought to change the effects of PBL approach have been determined. These
are the fields of science, the education level of students, sample size, time, methods, and the types of
publication used in the studies. Otherwise, intermediate variables related with the person prepared
the achievement test and operator was desired to included to study but wasn’t included due to the
fact that informations weren’t given or precence of much difference between number of studies in sub
groups. Under general purpose, it has been tried to identify the differences between the studies with
meta-analysis characteristics and the PBL approach’s effect size. Thus, the following questions are
tried to be answered:
1) What is the effect of PBL approach on the students’ academic achievements in science
classes?
2) Does differ impact on the academic achievement of students of PBL approach by academic
achievement of students in fields of science (Physics, Chemistry, Biology, Field of General
Science)?’’
3) Does differ impact on the academic achievement of students of PBL approach by education
levels (Primary, secondary, high school, bachelor)?
4) Does differ impact on the academic achievement of students of PBL approach by sampe
size in studies (1-50 students, more than 50 students)?
5) Does differ impact on the academic achievement of students of PBL approach by practice
time (1-20 hours, more than 20 hours)?
6) Does differ impact on the academic achievement of students of PBL approach by methods
used in studies (only PBL method, another extra method with PBL method)?
7) Does differ impact on the academic achievement of students of PBL approach by types of
publication (master thesis, PhD dissertation, article)?
Method
This part includes research model used in study, data collection, inclusion criteria, coding of
datas, analyzing and commenting of datas.
Research Model
In this research meta-analysis method used to designate of PBL approach’s effect. Meta-
analysis is a literature search method in scientific research. Meta-analysis is a statistical procedure
application used for the synthesis and comment of individuals studies. Meta-analysis provide
comparison and combination of experimental studies findings in a similar area by statistical methods
consistent and coherent way and calculation the effect size (Cohen, Manion & Morrison, 2007; Ergene,
1999; Glass, 1976; Hunter & Schmidt, 1990).
Data Collection
The studies included to research, is formed from master and doctoral theses, articles
published or not published in refereed scientific journals between 2002-2013 in Turkey as “PBL
Approach” and own research problems and needed statistical datas.
Search of postgraduate theses in Turkey was carried out between the dates of 01.06.2013 and
22.02.2013 as Turkish and English from Council of Higher Education National Theses Centre web site.
In search, theses that have that have “project based learning”, “project founded learning”, “project
approach” and “project based” at headlines and key words in Turkish or English were listed. It has been

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reached 108 theses names as a result of listing. As a result of investigations, theses suitable for research
problem were included study. Investigations were made by examining of the full text. 46 theses
prepared outside of field of science have been found. 17 restricted theses and 12 theses could not find
in centre were requested from writer or the university libraries. It has been reached to seven thesis by
this way but could not be reached 2 thesis in any way. In this process, it has been reached 38 theses
about our subject affecting of academic achievement of students’ in science classes by PBL approach.
These theses have been inserted to meta-analysis study.
Scanning literature to reach articles that published in Turkey has been done between June
2013 and February 2014 at ULAKBIM that the overall scientific journals in Turkey indexed, ASOS and
refereed scientific journals to reach articles which published in Turkey. Theses wee searched
oppositely since theses in Turkey is also published as an article. At the end of the search 2 articles
were included to study which are done as PBL approach’s about academic achievement of students’ in
science classes.
In one of the theses about academic achievement is included 2 different studies. So 2 effect size
values have calculated in this study and inserted to meta-analysis study in this way.
Inclusion Criteria
The inclusion criteria of inserted studies are:
1) Done between years of 2002-2013 of study in Turkey.
2) Published as master, doctoral theses or article in scientific journals which written in
languages of Turkish or English of study.
3) Being experimental of study.
4) Application of PBL approach to experimental group, traditional method is to control
group.
5) Being arithmetic average and standart deviation values has been about academic
achievement of students’ in science classes at experimental and control groups.
6) Giving sample values at studied groups.
Codification of Datas
Reliability of coding is an important point in the meta-analysis. Therefore, all studies should
be evaluated by at least two experts (Açıkel, 2009; Akçil & Karaağaoğlu, 2001). Codification form
(appendix-1) was prepared by researchers for determination of whether or not suitable for include in
meta-analysis and comparement between meta-analysis for the purpose of study. Informations in
codification form has chosen general characteristics of study. Some of the features in codification
forms are; name of the study, writer of the study, type of the study, publishment year of study, the
scale used in the study by whom, practice time, city of the study applied, education level of students,
statistical datas in the study, effect size of the study.
For reliability of the study, codifications must be done at least two other researchers.
Codifications were done by two researchers. Number of codes which are equal to each other clearized
by comparing of two researchers who have completed their master's degree in educational sciences
and doctoral studies are continuing. The reliability of the study found %97 by using reliability level
formula (Miles & Huberman, 2002). %70 and over values obtained from this formula are found
reliable enough for it (Yıldırım & Şimşek, 2011, p. 233). So it can be said that the codifications is
reliable. The codes which are not equal checked and corrected by two researchers by common consent.

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Analyzing and Commenting of Datas
In this study transaction effect meta-analysis is used in analyzing of datas. This technique
developed by Glass, take an important place in education practices, social sciences and psychology
researches. The relation of this type meta-analysis summarizes as transaction effect, the relation of the
effects, nature of the object, quantity of the transaction and effect factors.
At transaction effect meta-analysis, it can be used starndardized effect size which shows
Cohen d. It is determined by division of difference between experimental group and control group to
combined standard deviation (
2)1()1( 22



ec
eecc
Nnn SnSn
S
) (Cohen d
N
ce
SXX 

) (Huffcutt, 2002; Lipsey ve Wilson, 2001; Schulze, 2004). This statistical method
provides a comparison of the resulting effect size by used in multiple studies to work independently
of the data to be converted into a common measurement system. At the same time, power analysis
should be performed that indicates the possibility of identifying obtained effect size correctly
(Borenstein, Hedges, Higgins & Rothstein, 2009; Ellis, 2010; Üstün & Eryılmaz, 2014). Power analysis
is done by using in NORMSDIST formula function in Excel.
The scales can not be same in studies and can have inconsistent values which included into
research. For that difference between groups which PBL approach used or did not use by standard for
suitable in meta-analysis statistics studies with sample method, used standardized arithmetic average
differences effect size (Cohen, 1988; Huffcutt, 2002; Hunter & Schmidt, 1990; Lipsey & Wilson, 2001;
Rosenthal, 1991; Schulze, 2004; Wolf, 1986). Different researches are seen on the content of the studies
included in this meta-analysis study. Obtained effect sizes using different tests on different samples in
studies were calculated separately. Weights of studies were calculated as relative weights.
Classifications are used when commenting importance of effect size obtained from meta-
analysis. Effect size classification by Cohen and others are as follows (2007, p. 521):
 0 ≤ Effect size value ≤ 0,20 “poor”,
 0,21 ≤ Effect size value ≤ 0,50 “modest”,
 0,51 ≤ Effect size value ≤ 1,00 “moderate”,
 1,01 ≤ Effect size value has “strong” effect level.
Studies is determined to be included in meta-analysis by analysing of research subject being
scanned quantitatively and qualitatively, it was aimed to reduce the quality problem by including
only theses and articles in the study. Related to opinions of experts that primary studies should not be
evaluated based on the single quality scale score and therefore studies should not be taken out of the
meta-analysis (Üstün & Eryılmaz, 2014; Wells & Littel, 2009). After this stage, the statistical
combination of results is required. Before calculation of effect sizes calculated which statistical model
will be used is decided that Hedges and Olkin (1985)'s described by Q statistics (tests used in measure
of homogenity of effect size and population sample) in meta-analysis. There two models; fixed effect
and random effect model.

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It is assumed that only one real effect size for each run in fixed effect model (Borenstein et al.,
2009). If effect size varies between studies for some reason it is called as sampling error (Borenstein,
Hedges, Higgins & Rothstein, 2013). Random effect model is the model that estimates the average
effect size of studies (Borenstein et al., 2013). In each study factors affecting operation probably will
vary. If the existence of these differences is important to use a random effects model would be more
appropriate.
Other statistics related to the heterogeneity of the studies together with Q statistic are also
available. I2 developed as a complement of the Q statistics for heterogeneity of results may give a
clearer result (Petticrew & Roberts, 2006). I2 shows heterogeneity due to 25% low heterogeneity, 50%
intermediate and 75% of high heterogeneity (Cooper et al., 2009, p. 263).
Study number required for changing significance of results about studies’ effect size, which
included to meta-analysis, analysed with Orwin method. Number of studies that average effect size
value is zero is can be calculated by Orwin method (Hunter & Schmidt, 1990; Lipsey & Wilson, 2001).
Orwin is calculated depending to the practical significance and also gives the chance of finding to
researchers working only with missing studies and studies included in the meta-analysis of the overall
effect size will decrease the value of the specific effect size (Üstün & Eryılmaz, 2014). This finding
gives idea about effect size reliability which resultant as meta-analysis. In addition, funnel plot was
used as to whether publication bias. Possible loss of the number of studies in meta-analysis and
estimated effect of these studies on general effect was calculated by using trimm and fill method at
funnel plot.
In this meta-analysis study PBL approach effects and traditional education methods effects
were compared. In the study, PBL approach and traditional education methods were taken as
independent variable, academic achievement of students in science classes is dependent variable.
Analog ANOVA was used in analysis of intermediate variables.
Comprehensive Meta-Analysis 2.0 (CMA), MetaWin and Excel programmes were used in
analyzing of datas. CMA was used for the overall effect size, sub-group analysis, publication bias,
drawing of the forest plot and funnel plot graphs. MetaWin was used for normal quantile plot. Excel
was used for power analysis.

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Results
In this part, results about meta-analysis are given. Meta-analysis of the problems of research
results are mentioned obtained by the method of combining the analysis results and their
interpretation.
General Effect Size Results
Meta-analysis results given in there which are about PBL approach and traditional education
methods effects in academic achievement of students in science classes.
Firstly, we have to determine the meta-analysis model to calculate effect size of studies. First
we have to test homogenity of the studies by using fixed effect model.
Results about homogenity of the studies and general effect size by using the model of fixed
effect model given in Table 1:
Table 1. The Results of Studies’ Effect Size Based on Fixed Effect Model
Average
Effect Size
Value (ES)
Degrees of
Freedom
(df)
Homogenity
Value (Q)
Chi-Square
Table Value
(Chi-Square)
Standard
Error (SE)
I2
%95 Confidence Interval
for Effect Size
(ES (%95 CI))
Minimum
Value
(Min.)
Maximum
Value
(Max.)
0,895
41
271,800
56,942
0,043
84,92
0,811
0,979
When we calculate homogenity value of studies based on fixed effect model, we found it
Q=271,800. In  table significance level of %95 for forty-one degree of freedom value found as 56,942.
Statistical value of Q=271,800 passed over forty-one degree of freedom value (for df=41,
56,942). Likewise, nearly %85 with I2 was highly heterogeneous. With this result studies’ effect
size is heterogeneous by fixed effect model. So that there is not only one real effect under effect size
value.
For fixed effect model studies seems heterogeneous, misleadings can removed by using
random effect model. Results about homogenity of the studies and general effect size by using the
model of random effect model given in Table 2:
Table 1. The Results of Studies’ Effect Size Based on Random Effect Model
Average Effect
Size Value (ES)
n
Standart
Error (SE)
Z
p
%95 Confidence Interval for
Effect Size
(ES (%95 CI))
Minimum
Value (Min.)
Maximum
Value (Max.)
0,997
42
0,112
8,880
0,000
0,777
1,218
For analysis result of random effect model, average effect value is 0,997 with standard error of
0,112. In %95 confidence interval, minimum value of effect size is 0,777 and maximum value of effect
size is 1,218. When we look statistical significance, it is found as Z=8,880 ve p=0,000. So the result is
significance as statistical. Value was found 0,986 as a result of power analysis. This is a high value and
can be said that determined the real effect of the study correctly.

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Average effect size value is positive (+0,997), so transaction effect is in favor of experimental
group. So that PBL approach has positive effect on students’ academic achievement on science classes.
This effect is nearly strong effect for Cohen and his friends classifications (2007).
Forest plot that shows distribution of effect size values of primary studies formed by random
effect model is given in Figure 1.
Figure 1. Forest plot showing distribution effect size values of studies
Squares in the plot shows study’s effect size, square lines on either side of squares indicate
95% confidence interval of the effect size minimum and maximum limits. They belong to the square of
the field study indicates the weight of the overall effect size. The die having a rhombic shape located
below shows overall effect size of studies.
When we examine effects size of studies, it determined minimum effect size value is -0,423,
maximum effect size is 2,862. When we look effect size of studies, 39 studies are pozitive, 3 studies are
negative from 42 studies. 39 studies which have pozitive effect in favor of experimental group using
PBL approach, 3 studies have negative effect in favor of control group using traditional education
method.
General distribution of studies’ effect size are normal distribution because they are on
confidence interval which around x=y lines and show in cutted points. Effect size of studies’, which
included this research, normal distribution graph given in Figure 2.
Calisma Adi Statistics for each study Std diff in means and 95% CI
Std diff Standard Lower Upper Relative Relative
in means error limit limit p-Value weight weight
Özcan 1,827 0,394 1,054 2,599 0,000 2,12
Altuntas Nikbay 0,523 0,328 -0,120 1,166 0,111 2,31
Demir 0,871 0,307 0,270 1,473 0,005 2,37
Girgin 0,570 0,220 0,138 1,001 0,010 2,59
Erdogan 0,122 0,225 -0,319 0,564 0,587 2,58
Güven 1,912 0,252 1,418 2,406 0,000 2,51
Avci 1,739 0,429 0,899 2,580 0,000 2,03
Dogay 1,157 0,279 0,610 1,704 0,000 2,44
Tuncer -0,061 0,277 -0,604 0,483 0,827 2,45
Seloni 1,944 0,394 1,172 2,717 0,000 2,12
Z.Gültekin 0,436 0,266 -0,084 0,957 0,101 2,48
Serttürk 1,107 0,240 0,636 1,577 0,000 2,54
Denis Çeliker 1,322 0,303 0,728 1,917 0,000 2,38
Degirmenci 0,766 0,332 0,115 1,416 0,021 2,30
Dilseker 0,374 0,311 -0,237 0,984 0,230 2,35
Ekiz 0,215 0,263 -0,301 0,731 0,415 2,48
Dogan 2,862 0,374 2,130 3,595 0,000 2,18
Karacalli 1,884 0,201 1,490 2,278 0,000 2,63
Köse 1,609 0,319 0,983 2,234 0,000 2,33
Yurttepe 1,879 0,380 1,135 2,623 0,000 2,16
Özbek 0,755 0,175 0,412 1,098 0,000 2,69
Imer 2,384 0,386 1,628 3,140 0,000 2,15
Özahioðlu 0,336 0,244 -0,143 0,815 0,169 2,53
Simsek Öztürk 0,824 0,253 0,329 1,319 0,001 2,51
Çil-1 1,712 0,350 1,026 2,398 0,000 2,25
Çil-2 0,084 0,302 -0,509 0,676 0,782 2,38
Gelisgen 2,418 0,381 1,672 3,164 0,000 2,16
Toprak 0,411 0,226 -0,032 0,854 0,069 2,58
Baran-1 1,056 0,397 0,279 1,834 0,008 2,12
Kocak 1,001 0,402 0,213 1,788 0,013 2,10
Benzer 0,533 0,237 0,068 0,998 0,025 2,55
Baran-2 1,498 0,274 0,960 2,036 0,000 2,45
Çakallioglu 0,617 0,256 0,116 1,119 0,016 2,50
Keser 1,573 0,362 0,863 2,282 0,000 2,21
Keskin 0,634 0,214 0,215 1,053 0,003 2,60
Zeren Özer -0,423 0,333 -1,075 0,229 0,203 2,30
Altun Yalcin 1,770 0,249 1,282 2,258 0,000 2,52
Bagci -0,369 0,248 -0,856 0,118 0,138 2,52
Ayan 0,194 0,247 -0,290 0,678 0,432 2,52
M.Gültekin 0,776 0,306 0,176 1,375 0,011 2,37
Korkmaz 0,810 0,254 0,312 1,309 0,001 2,51
Yurdatapan vd. 1,443 0,391 0,677 2,209 0,000 2,13
0,997 0,112 0,777 1,218 0,000 -4,00 -2,00 0,00 2,00 4,00
Favours A Favours B
Meta Analysis
Meta Analysis

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Figure 2. Effect Size’s Normal Quantile Plot
When we look normal quantile plot of studies’ effect size, they are close to normal distribution
line and don’t pass over the defined borders. Therefore studies which included to study show normal
distribution.
General effect size value of impact of project-based learning approach to students' academic
achievement in science classes is 0,997 at moderate level. To drop this level to modest level, needed
number of studies found 41 which’s effect size values are zero. To drop this level to poor level, needed
number of studies found 167 which’s effect size values are zero. To drop this level to zero (0,01),
needed number of studies found 4146 which’s effect size values are zero. Referring to the excess of the
number of studies that can be said obtained the results of analyze is reliable and publication bias is
low. Moreover, whether publication bias can be interpreted with the aid of Funnel Plot given in Figure
3.
Figure 3. Effect Size’s Funnel Plot
-3 -2 -1 0 1 2 3
0,0
0,1
0,2
0,3
0,4
0,5
Standard Error
Std diff in means
Funnel Plot of Standard Error by Std diff in means

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In the case of publication bias, effect sizes are take place in an distribution way in the funnel
plot. In the case of the absence of publication bias, effect sizes are take place in a symmetrical
distribution. However, exact symmetry is seen in case of the addition of four studies to the left side of
funnel plot formed by Duval and Tweedie’s trimm and fill method. This is one of the evidence that the
publication bias is low. Adjusted mean effect size value was found to be 0.819.
Results About Problem of Studies’ Fields of Science
The result of whether the effect sizes differs or not according to the fields of science is given in
terms of academic achievement in Table 3.
Table 3. Effect Size Differences According to Fields of Science
Variable
Inter-Group
Homogeneity Value (QB)
p
n
ES
ES (%95 CI)
Standard
Error (SE)
Min.
Max.
Field of
Science
0,594
0,898
Physics
20
1,046
0,718
1,374
0,167
Chemistry
5
0,873
0,213
1,534
0,337
Biology
16
0,954
0,589
1,319
0,186
General
1
1,443
-0,103
2,989
0,789
Established groups, according to the fields of science, this research has been done with three
fields of science in, called as general. Critic value with three degree of freedom found 7,815 on table
with %95 significance level. The homogeneity value between the groups, which was built in according
to fields of science, has been found as (QB) 0,594. Because of the homogenity value between the groups
is smaller than the critical value, has not been found statistically significant differences between the
groups which formed for the fields of science.
Results About Problem of Target Group’s Education Level in Studies
The result of whether the effect sizes differs or not according to the education level is given in
terms of academic achievement in Table 4.
Table 4. Effect Size Differences According to Target Group’s Education Level
Variable
Inter-Group
Homogeneity Value (QB)
p
n
ES
ES (%95 CI)
Standard
Error (SE)
Min.
Max.
Education
Level
5,124
0,163
Primary
3
1,417
0,618
2,216
0,408
Secondary
26
0,979
0,708
1,249
0,138
High School
4
1,536
0,826
2,247
0,362
University
9
0,680
0,221
1,139
0,234
Critic value with one degree of freedom found 3,841 on table with %95 significance level.
The homogeneity value between the groups, which was built in according to education level, has been
found as (QB) 5,124. Because of the homogenity value between the groups is smaller than the critical
value, has not been found statistically significant differences between the groups which formed for
education level.

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Results About Problem of Sample Sizes of Studies
The result of whether the effect sizes differs or not according to the sample size is given in
terms of academic achievement in Table 5.
Table 5. Effect Size Differences According to Sample Sizes
Variable (Number
of Students)
Inter-Group Homogeneity
Value (QB)
p
n
ES
ES (%95 CI)
Standard
Error (SE)
Min.
Max.
Sample Size
0,340
0,560
1≤N≤50
18
1,078
0,728
1,428
0,179
51≤N
24
0,944
0,656
1,231
0,147
Critic value with one degree of freedom found 3,841 on table with %95 significance level.
The homogeneity value between the groups, which was built in according to sample sizes, has been
found as (QB) 0,340. Because of the homogenity value between the groups is smaller than the critical
value, has not been found statistically significant differences between the groups which formed for
sample size.
Results About Problem of Practicing Time of Studies
The result of whether the effect sizes differs or not according to the practicing time is given in
terms of academic achievement in Table 6.
Table 6. Effect Size Differences According to Practicing Time
Variable
(Lesson Hour)
Inter-Group
Homogeneity Value (QB)
p
n
ES
ES (%95 CI)
Standard
Error (SE)
Min.
Max.
Practicing
Time
3,492
0,174
1≤h≤20
17
1,203
0,851
1,556
0,180
21≤h
15
1,004
0,632
1,376
0,190
Unspecified
10
0,662
0,218
1,107
0,227
Critic value with two degree of freedom found 5,991 on table with %95 significance level.
The homogeneity value between the groups, which was built in according to practicing time, has been
found as (QB) 3,492. Because of the homogenity value between the groups is smaller than the critical
value, has not been found statistically significant differences between the groups which formed for
practicing time.
Results About Problem of Methods Used in Studies
The result of whether the effect sizes differs or not according to the methods used in studies is
given in terms of academic achievement in Table 7.
Table 7. Effect Size Differences According to Methods Used
Variable
Inter-Group
Homogeneity Value (QB)
p
n
ES
ES (%95 CI)
Standard
Error (SE)
Min.
Max.
Method
0,002
0,961
PBL
36
0,996
0,755
1,236
0,123
PBL and
others
6
1,012
0,423
1,601
0,301
Critic value with one degree of freedom found 3,841 on table with %95 significance level.
The homogeneity value between the groups, which was built in according to methods used in studies,
has been found as (QB) 0,002. Because of the homogenity value between the groups is smaller than the

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critical value, has not been found statistically significant differences between the groups which formed
for the methods used in studies.
Results About Problem of Types of Publication
The result of whether the effect sizes differs or not according to the types of publication is
given in terms of academic achievement in Table 8.
Table 8. Effect Size Differences According to Types of Publication
Variable
Inter-Group
Homogeneity Value (QB)
p
n
ES
ES (%95 CI)
Standard
Error (SE)
Alt
Üst
Type of
Publication
0,475
0,789
Master Thesis
30
1,043
0,777
1,310
0,136
PhD Thesis
9
0,926
0,448
1,405
0,244
Article
3
0,771
-0,076
1,617
0,432
Critic value with two degree of freedom found 5,991 on table with %95 significance level.
The homogeneity value between the groups, which was built in according to the types of publication,
has been found as (QB) 0,475. Because of the homogenity value between the groups is smaller than the
critical value, has not been found statistically significant differences between the groups which formed
for the types of publication.
Number of studies and mean effect sizes of all study characteristics based on subgroup
analyzes are given in Table 9.
Tablo 9. Number of studies and Effect Sizes Related to Characteristics
Variable
n
ES
SE
Field of Science
Physics
20
1,046
0,167
Chemistry
5
0,873
0,337
Biology
16
0,954
0,186
General
1
1,443
0,789
Education Level
Primary
3
1,417
0,408
Secondary
26
0,979
0,138
High School
4
1,536
0,362
University
9
0,680
0,234
Sample Size
1≤N≤50
18
1,078
0,179
51≤N
24
0,944
0,147
Practicing Time
1≤h≤20
17
1,203
0,180
21≤h
15
1,004
0,190
Unspecified
10
0,662
0,227
Method
PBL
36
0,996
0,123
PBL and others
6
1,012
0,301
Type of Publication
Master Thesis
30
1,043
0,136
PhD Thesis
9
0,926
0,244
Article
3
0,771
0,432
The table which contains the studies with its variables is on appendix-2.

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Discussion, Conclusion and Recommendations
As happens in any study, in this meta-analysis has some limitations. First of these is the
limitations meta-analysis method has itself. Control grouped empirical studies which contains pre test
and final test has been included into the study. An analysis could have been done about quality by
using high validity and reliability quality scales. This study is consisted of researches have been done
in Turkey. With the study it has been aimed to contribute to the national education policy. The results
can ony be generalized for Turkey. The other limitation is at subgroup analysis, ANOVA, which can
be effected from different factors, was used. And also the study has limitation of intermediate
variables analysis which are coded. Also, rarity of primary numbers in some subgroups could be
affected results.
First question of study is “What is the effect of PBL approach on the students’ academic
achievements in science classes?” Totally 42 studies stated about effect of PBL approach to students'
academic achievement in science lessons. Total sample size in studies is (total sample size in
experimental and control groups) 2558. When we calculate homogenity value of studies based on
fixed effect model, we found it Q=271,800. In  table significant level of %95 for forty-one degree of
freedom value found as 56,942. Statistical value of Q=271,800 passed over forty-one degree of freedom
value (for df=41, 56,942). So we used random effect model to calculate effect size of studies. It
is determined that PBL approach have a positive effect to students 'academic achievement in science
classes in order to determine its effect on the results of the meta-analysis of the PBL approach based
on traditional learning methods to students' academic achievement in science classes. The effect size of
the PBL approach, between 0,777-1,218 confidence interval, has been found 0,997 (%95 CI, SE=0,112)
about the academic achievements of the students in science classes by using random effect model. This
value is moderate level to Cohen, Manion and Morrison’s the classification of the effect size (2007). In
the Kaşarcı’s meta-analysis study (2013), which was practised to prove the effect of PBL approach in
academic achievement in field of science, the effect size value is between 0,763-1,273 confidence
interval has been found ES=1,018 and seen compatible with this study. This effect is very close to
strong level. According to studies about studies of PBL approach that applied 2558 people, PBL
approach is more effective in increasing the academic achievement of students in science classes,
compared to traditional teaching methods. In comparison with the traditional teaching approaches,
PBL approach is more effective in developing academic achievement of the students in science classes.
39 studies are pozitive and 3 studies are negative in 42 studies. It could not determine why 3 negative
studies are in favor for traditional education methods, but it considered, iti is about operator error.
There are 4146 studies needed which’s effect size values are zero that decrease the effect size value to
0,01 which united 42 studies with meta-analysis method. It can be said results of analyses are reliable
when we look number os studies are more.
Second question of study is “Does differ impact on the academic achievement of PBL
approach by academic achievement of students in fields of science (Physics, Chemistry, Biology, Field
of General Science)?’’ There are 20 studies in physics, 16 studies in biology, 5 studies in chemistry and
1 study in general science. When average effect size of fields of science are compared, it has been
observed that the highest effect size value is in field of general science (ES=1,443), the lowest effect size
value is in chemistry (ES=0,873). When we look homogenity value between groups (QB=0,594) it seems
it is little from critic value at %95 significance level as three degrees of freedom (df=3 için 7,815).
Therefore, there could not find a statistically significant difference between groups which formed for
fields of science. According to that fields of science could not change PBL approach’s effect size as a
significant difference. Considering the results of the analysis according to the science field, the highest
effect size value is seen as 1 study in general science covering all fields of science (ES=1,443). Effect size

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of the main areas of science is seen as close to each other at the same time, strong (ES=1,046) in the
physics field, moderate in the biological (ES=0,954) and chemical fields (ES=0,873).
Third question of study is “Does differ impact on the academic achievement of students of
PBL approach by education levels (Primary, secondary, high school, bachelor)?’’ There are 26 studies
in secondary school level, 9 studies in university level, 4 studies in high school level and 3 studies in
primary school level. When average effect size of students’ education level are compared, it has been
observed that the highest effect size value is in high school level (ES=1,536), the lowest effect size value
is in university level (ES=0,680). When we look homogenity value between groups (QB=5,124) it seems
it is little from critic value at %95 significance level as three degrees of freedom (df=1 için 3,841).
Therefore, there could not find a statistically significant difference between groups which formed for
students’ education level. According to that students’ education level could not change PBL
approach’s effect size as a significant difference. However it has been observed that the difference
between the effect sizes of the groups is not small. Considering the results of the analysis according to
the educational level of the working group, the highest effect size values are observed in high school
(ES=1,536) and primary school (ES=1,417) at strong level. Doing less number of primary studies at this
level may have impact on these results. It can be said that effect size is also high at secondary school
level (ES=0,979) and the results are reliable in view of much number of primaryb studies. The lowest
effect size values was specified in universities (ES=0,680) at medium level.
Fourth question of study is “Does differ impact on the academic achievement of students of
PBL approach by sampe size in studies (1-50 students, more than 50 students)?” There are 24 studies
in “more than 50 students”, 18 studies in “1-50 students”. When average effect size of sample size are
compared, it has been observed that the highest effect size value is in “1-50 students” (ES=1,078), the
lowest effect size value is in “more than 50 students” (ES=0,944). When we look homogenity value
between groups (QB=0,340) it seems it is little from critic value at %95 significance level as one degree
of freedom (df=1 için 3,841). Therefore, there could not find a statistically significant difference
between groups which formed for sample size. According to that sample size could not change PBL
approach’s effect size as a significant difference. However the effect size of the groups close to each
other. Considering the results of the analysis based on the sample size of the study group, it is
observed that effect size values of either sub variants are border of strong level.
Fifth question of study is “Does differ impact on the academic achievement of students of
PBL approach by practice time (1-20 hours, more than 20 hours)?” There are 17 studies in “1-20
hours”, 15 studies in “more than 20 hours” and 10 studies that application time was unspecified.
When average effect size of practice time are compared, it has been observed that the highest effect
size value is in “1-20 hours” (ES=1,203), the lowest effect size value is in studies that application time
was unspecified (ES=0,662). “more than 20 hours” (ES=1,004). When we look homogenity value
between groups (QB=0,002) it seems it is little from critic value at %95 significance level as two degree
of freedom (df=2 için 5,991). Therefore, there could not find a statistically significant difference
between groups which formed for practice time. According to that practice time could not change PBL
approach’s effect size as a significant difference. However the effect size of the groups is close to each
other. Considering the results of the analysis carried out according to application times, it was
determined that application times of 10 studies was unspecified. Effect size value (ES=0,662) of the
studies which application times was unspecified was determined as low in regard to other two sub
groups. Also, effect size values of other two sub groups can be shown as strong level.
Sixth question of study is “Does differ impact on the academic achievement of students of PBL
approach by methods used in studies (only PBL method, another extra method with PBL method)?”
There are 36 studies in “used only PBL method”, 6 studies in “another extra method used with PBL

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method”. When the average effect sizes of used methods are compared, it has been observed that the
highest effect size value is in “another extra method used with PBL method” (ES=1,012), the lowest
effect size value is in “used only PBL method” (ES=0,996). When we look homogenity value between
groups (QB=0,002) it seems it is little from critic value at %95 significance level as one degree of
freedom (df=1 için 3,841). Therefore, there could not find a statistically significant difference
between groups which formed for used methods. According to that used methods could not change
PBL approach’s effect size as a significant difference. However the effect size of the groups is close to
each other. When considering the result of the analysis with respect to the methods used, there are 6
study of PBL approach together with another methods and 36 study of only PBL approach applied. It
can be thought that differences between primary studies may affect the reliability of the results.
Besides, it can be shown that effect size of two sub groups are high and using another methods with
PBL approach doesn’t have a significant contributor.
The seventh question of the research is “Does differ impact on the academic achievement of
students of PBL approach by types of publication (master thesis, PhD dissertation, article)?” For this,
30 master theses, 9 PhD theses and 3 scientific articles are included to the meta-analysis. When the
average effect sizes of the types of publications are compared, it has been observed that master theses
have the highest effect value (ES=1,043), scientific articles have the lowest effect value (ES=0,771). As
the homogeneity value (QB=0,475) between groups is taken into consideration, this value has %95
percent significance level in Chi-square test table and with two unrestraint degree it is smaller than
the critical level (df=2 için 5,991). For this reason, a statistically significant difference has not
been found between the groups which formed for the types of publication. However it has been
observed that the difference between the effect sizes of the groups is excessive. Considering the results
of analysis according to types of publications, effect sizes of master theses (ES=1,043) and PhD
dissertations (ES=0,926) were observed as close to each other. Size effect values of articles (0,771) were
determined as low or medium levels in terms of theses.
Although there is no statistically significant difference according to the results; to increase
students’ academic achievement in science classes by using PBL approach would be more effective
physics as field of science, high school as education level and 1-20 hours as practice time.
Although there is no statistically significant difference according to the results; to increase
students’ academic achievement in science classes by using PBL approach would be less effective
chemistry as field of science, university as education level and more than 20 hours as practice time.
When the results examined, cause of PBL approach more effective in physics, it is more
connected in life from the other fields of science and people are more interactive with physics subjects
at daily life. PBL approach is more effective in high school level, because students can establish sincere
relations with their peers, due to their development period feature they can work effectively in project
studies groups. Especially students moves more independently at university level, project methods
are less effective for the students are this education level. Cause of PBL approach is more effective
between 1-20 hours as practice time, long-term study which is from limits of project methods cause
becoming less achievement in lessons. It has been seen that effect sizes of postgrad thesis were higher
than the article. These results can be considered normal because theses usually work with larger
sample sizes and rigorously.

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With the results and the experiment in study process in research, these recommendations to
be given to practitioners, program developers and researchers:
Recommendations to Practitioners
1) To determine PBL approach’s effect to students’ academic achievement in science classes
motivated meta-analysis study result; PBL approach is nearly at strong pozitive effect in
students’ academic achievement in science classes than traditional education methods.
Science teachers can use PBL approach for effective learning.
2) It identified that PBL approach has higher effect on students’ academic achievement in
physics. Therefore PBL approach specially can use in field of physics.
3) When we look PBL approach effect size on students education level, the highest effect size
is at high school level. According to that; PBL approach specially can use at high school
level to increase students’ academic achievement in science classes.
4) For sample size classification; there could not find significant difference in effect size of
PBL approach in students’ academic achievement in science classes. Therefore PBL
approach can be used classes which has different student present.
5) For practice time of studies; there could not find significant difference in effect size of PBL
approach in students’ academic achievement in science classes. Therefore PBL approach
can be used in different practice time. But due to it found it is more effective between 1-20
hours practice time, so project time don’t be extended unnecessarily.
6) It was determined that using another methods with PBL approach has no positive effect.
Therefore in lessons it is useful for learning to use another methods with PBL approach. So,
using another methods with PBL in lessons may not be created an important change.
Recommendations to Program Developers
1) There can be given more place to PBL approach because of pozitive effect of PBL approach
to students’ academic achievement in science classes. Specially cause of effect size found
high in physics and biology, there can be given more place in their curriculums. Effect size
value found less in chemistry than other fields of science. There can be given less place PBL
approach in chemistry curriculum.
2) It was determined that PBL approach increase students’ academic achievement in science
classes specially at high school level. Therefore there can be given more place to PBL
approach at high school level curriculums.

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Recommendations to Researchers
1) Studies with different effect size levels can be examined one by one and it can be
determined these differences effect from what sort of factors.
2) It has been found that effect sizes of postgrad theses were higher than the article. The
reasonf of that can be explored.
3) According to meta-analysis results, examining studies that have negative effect size value,
it can be researched negative effect what factors caused as.
4) There can be more studies about PBL approach in primary and high schools, then their
effect size can be analyzed again so it will be benefit for giving correct results.
5) There can be made more studies that used PBL approach in field of chemistry.
6) It is determined that to use another methods with PBL approach doesn’t increase effect size
value. Reason of this can be searched by detailed.
7) Studies about PBL approach included to meta-analysis generally made as level of
secondary school and university. There can be made researches with 4+4+4 education
system type.

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Appendix 1. Coding Form
1. Number of study:
2. Name of study:
3. Author/Authors of study:
4. Published year of study:
5. Type of publication of study:
6. Country of study:
7. City of study:
8. Practice time of study:
9. Who is prepared the test used in the study:
( ) Researcher ( ) Others
10. Name of lesson:
11. Subject of lesson:
12. Students’ education level:
( ) Primary ( ) Secondary ( ) High School ( ) University
13. Is there any method used with PBL approach in study?
( ) Yes ( ) No
14. Total sample size in study:
15. Descriptive statistics about achievement test for experimental and control groups
Experimental Group
Control Group
N
X
S
N
X
S
Pretest
Posttest
N:Sample, X: Arithmetic average, S: Standard Deviation
16. Effect size of study:

Education and Science 2014, Vol XX, No XXX, pp-pp
A. Authors
279
Appendix 2. Studies Included to the Meta-Analysis
No
Author, Year
ES
Name of Study
Publication
of Study
City of
Study
Target
Group Level
of the Study
Preparing
the Scale
Field of
Science
1
Rukiye
ÖZCAN, 2007
1,827
Effect of Project-Based Learning
Approach on Students' Academic
Achievement, Attitudes and
Opinions on Algal Biotechnology
Master
Thesis
Ankara
10th Grade
By the
researcher
Biology
2
Nergiz
ALTUNTAŞ
NİKBAY, 2009
0,523
Using the Method of Narration and
Project-Based Learning Methods
from the Perspective of Efficiency
Comparison of Student Achievement
Master
Thesis
Ankara
7th Grade
By the
researcher
Biology
3
Kenan
DEMİR, 2008
0,871
Effectiveness of Implementation
Integrated Curriculum with
Collaborative and Project-Based
Learning Approach
PhD Thesis
Ankara
4th Grade
By the
researcher
Physics
4
Derya
GİRGİN, 2009
0,570
Live and Life Unit of the Project-
Based Learning Approach
Elementary 5th Grade Students'
Effect on Academic Achievement
and Attitudes
Master
Thesis
İzmir
5th Grade
By the
researcher
Biology
5
Gülçin
ERDOĞAN,
2007
0,122
Topics in Environmental Education
Learning of Global Warming Effect
of Project-Based Learning
Master
Thesis
Zonguldak
University –
2th Grade
Not by the
researcher
Biology
6
Ezgi GÜVEN,
2011
1,912
Prediction-Observation-Explanation
Based on Environmental Education
Project Based Learning Method and
Method of Effect of Different
Variables Related to Student
Feedback
PhD Thesis
Ankara
University –
3th Grade
By the
researcher
Biology
7
Adem AVCI,
2006
1,739
Electronics Training Set Design with
Integrated Programming Software
Supported Project Based Learning
Effect on Development Students
Making Electronic Circuit Design
Performance and Retention
Master
Thesis
Adana
10th Grade
By the
researcher
Physics
8
Murat
TUNCER,
2007
-0,061
Electronic Circuits Course in Virtual
Environments Based on the Method
of Submission and Feedback of
Project Based Learning Effects on
Student Achievement
PhD Thesis
Elazığ
University –
2th Grade
By the
researcher
Physics

Education and Science 2015, Vol 40, No 178, 255-283
M. F. Ayaz & M. Söylemez
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No
Author, Year
ES
Name of Study
Publication
of Study
City of
Study
Target
Group
Level of the
Study
Preparing
the Scale
Field of
Science
9
Şirli Rahel
SELONİ, 2005
1,944
The Resulting Misconceptions
Remedy in Science Teaching with
Project-Based Learning
Master
Thesis
İstanbul
5th Grade
By the
researcher
Physics
10
Zeynep
GÜLTEKİN,
2009
0,436
Application of Project-Based
Learning Effect in Science Education
Students' Opinions Concerning the
Nature of Science, Science Process
Skills and Attitudes
Master
Thesis
İstanbul
6th Grade
By the
researcher
Physics
11
Meral
SERTTÜRK,
2008
1,107
Project-Based Learning Approach
Effect on Students' Achievement and
Attitude in Science Teaching 7th
Grade Science
Master
Thesis
İstanbul
7th Grade
By the
researcher
Biology
12
Huriye DENİŞ
ÇELİKER,
2011
1,322
Science and Technology of the Solar
System and Beyond: The Science of
Space Unit, Project-Based Learning
Applications Effect on Student
Achievement and Attitudes to
Science and Technology
PhD Thesis
İzmir
7th Grade
By the
researcher
Physics
13
Şerife
DEĞİRMENCİ
, 2011
0,766
Project-Based Learning Effect on
Student Achievement in Teaching
Unit's of Science and Technology at
the "Living Organisms and Energy
Relations"
Master
Thesis
Konya
8th Grade
By the
researcher
Biology
14
Zehra
DİLŞEKER,
2008
0,374
Using of Project-Based Learning
Methods Effect on Students'
Attitudes Toward Science and
Technology, Course Success and the
Elimination of Misconceptions in
Science and Technology Elementary
5th Grade
Master
Thesis
Manisa
5th Grade
By the
researcher
Physics
15
Kadriye
DOĞAN, 2008
2,862
Success of Project Based Learning
Effect in Teaching Concept on Cell
Subject
Master
Thesis
Afyonkarahis
ar
6th Grade
By the
researcher
Biology
16
Saide
KARAÇALLI,
2011
1,884
Project-Based Learning Methods’
Effect on Academic Achievement,
Attitudes and Retention in the 4th
Grade Science and Technology
Master
Thesis
Antalya
4th Grade
By the
researcher
Physics

Education and Science 2015, Vol 40, No 178, 255-283
M. F. Ayaz & M. Söylemez
281
No
Author, Year
ES
Name of Study
Publication
of Study
City of
Study
Target
Group
Level of the
Study
Preparing
the Scale
Field of
Science
17
Mehtap
YURDATAPA
N, İlknur
GÜVEN,
Fatma ŞAHİN,
2013
1,443
Project-Based Instruction Effect in
Elementary School 4th Grade
Students' Science Process Skills
Science and Technology
Article
İstanbul
4th Grade
Not by the
researcher
Physics,
Chemis
try and
Biology
18
Mücahit
KÖSE, 2010
1,609
Project-Based Learning Approach
Effect on Students' Achievement and
Attitudes in Teaching 7th Grade
Science and Technology Courses
"Force and Motion" Unit
Master
Thesis
Konya
7th Grade
By the
researcher
Physics
19
Saide
YURTTEPE,
2007
1,879
Project-Based Learning Effect on
Student Achievement in Primary
Science Course
Master
Thesis
Eskişehir
8th Grade
Not by the
researcher
Biology
20
Özden
ÖZBEK, 2010
0,755
Investigation of the Primary Global
Warming Topics in Science and
Technology in the Project-Based
Instruction Model
Master
Thesis
Malatya
7th Grade
By the
researcher
Biology
21
Nagihan
İMER, 2008
2,384
Investigation of the Project-Based
Learning Approach Effect on
Students' Academic Achievement
and Attitude in Primary Science and
Technology Education
Master
Thesis
Ankara
6th Grade
By the
researcher
Physics
22
Burak
ÖZAHİOĞLU,
2012
0,336
Project-Based Learning Effect on
Scientific Process Skills,
Achievement and Attitudes in
Elementary Science and Technology
Courses
Master
Thesis
Çanakkale
6th Grade
Not by the
researcher
Biology
23
Elif KESKİN,
2011
0,634
Investigation of the Effects of
Project-Based Learning Method to
Science Secondary School Students'
Achievement and Motivation
Master
Thesis
Bursa
6th Grade
By the
researcher
Physics
24
Dilek ZEREN
ÖZER, 2011
-0,423
Project-Based Learning Effect to
Science Teachers' Achievement and
Development of Science Process
Skills in Biology Subjects
PhD Thesis
Bursa
University –
2nd Grade
By the
researcher
Biology

Education and Science 2015, Vol 40, No 178, 255-283
M. F. Ayaz & M. Söylemez
282
No
Author, Year
ES
Name of Study
Publication
of Study
City of
Study
Target
Group
Level of the
Study
Preparing
the Scale
Field of
Science
25
Sema ALTUN,
2008
1,770
Investigation of Project-Based
Learning Methods Effect to Students’
Academic Achievement of Electrical
Topic, Attitudes Toward Physics and
Science Process Skills
PhD Thesis
Erzurum
University –
1st Grade
Not by the
researcher
Physics
26
Uğur BAĞCI,
2005
-0,369
Investigation of Project-Based
Learning Method Effect Students'
Achievement Levels Applied in the
Teaching of Elementary Science
Master
Thesis
Konya
8th Grade
Not by the
researcher
Physics
27
Mesude
AYAN, 2012
0,194
Project-Based Learning Approaches
Effect to Students' Academic
Achievement Level in Science
Primary School
Article
Ankara
5th Grade
By the
researcher
Physics
28
Mehmet
GÜLTEKİN,
2007
0,776
The Effect of Project Based Learning
on Learning Outcomes in the Fifth-
Grade Science Education
Article
Eskişehir
5th Grade
By the
researcher
Physics
29
Hünkâr
KORKMAZ,
2002
0,810
Project-Based Learning Approach
Effect on Science Education
Elementary School Students'
Academic Achievement, Academic
Self-Concept and Its on Work Time
PhD Thesis
Ankara
7th Grade
By the
researcher
Chemis
try
30
Kemal Şahin
KESER, 2008
1,573
Project-Based Learning Approach
Effect in Science Course
Achievement, Attitude and Learning
Persistent
Master
Thesis
Eskişehir
8th Grade
By the
researcher
Biology
31
Gülden
DOĞAY, 2010
1,157
Project-Based Learning Methods
Effect on Student Achievement in
Ecology Unit of Learning
Master
Thesis
Ankara
10th Grade
By the
researcher
Biology
32
Aykut ÇİL,
2005
1,712
0,084
Project-Based Learning in Chemistry
Education Assessment and
Recommendations
Master
Thesis
Eskişehir
7th and 8th
Grade
By the
researcher
Chemis
try
33
Mustafa
GELİŞGEN,
2007
2,418
Project Based Curriculum
Development on Vocational and
Technical Secondary Education
Master
Thesis
Afyonkarahis
ar
10th Grade
By the
researcher
Physics

Education and Science 2015, Vol 40, No 178, 255-283
M. F. Ayaz & M. Söylemez
283
No
Author, Year
ES
Name of Study
Publication
of Study
City of
Study
Target
Group
Level of the
Study
Preparing
the Scale
Field of
Science
34
Serhat Onur
EKİZ, 2008
0,215
Science and Technology Laboratory,
supported by the Project-Based
Learning Approach Effect Level of
Teaching on Student Achievement,
Retention and Affective
Characteristics Investigation
Master
Thesis
Muğla
University –
2th Grade
By the
researcher
Biology
35
Elif TOPRAK,
2007
0,411
Project-Based Learning Approach
Effect on Elementary 5th Grade
Students' Academic Achievement in
Science and Technology
Master
Thesis
İstanbul
5th Grade
By the
researcher
Physics
36
Medine
BARAN, 2007
1,056
A Study on the Effect Project-Based
Learning Model of Physical
Education and Second Grade
Students' Achievement and
Attitudes in Physics Electrostatic
Topics
Master
Thesis
Diyarbakır
University –
2nd Grade
By the
researcher
Physics
37
Ayşe ŞİMŞEK
ÖZTÜRK,
2008
0,824
Project-Based Learning Method
Effect on Student Achievement Level
in the Teaching of 7th Grade
Students "Journey to Inner Structure
of Matter" unit
Master
Thesis
Konya
7th Grade
By the
researcher
Chemis
try
38
İlknur
KOÇAK, 2008
1,001
Evaluation of Project-Based Learning
Model Effect to Understanding of
Students in Chemical Education with
Alkenes Topics and Attitudes
Towards Chemical and
Environmental
Master
Thesis
Ankara
University –
2nd Grade
By the
researcher
Chemis
try
39
Elif BENZER,
2010
0,533
Project-Based Learning Approach
Prepared Environmental Education
Course Effect to Teachers of Science
Literacy on the Environment
PhD Thesis
İstanbul
University –
2nd Grade
By the
researcher
Biology
40
Medine
BARAN, 2011
1,498
Technology and Project-Based
Learning Approach Based Thinking
of Journey Technical Effect on High
School 11th Grade Students'
Achievement in Physics and Its
Academic Self-Concept
PhD Thesis
Diyarbakır
11th Grade
By the
researcher
Physics
41
Sıdıka Nazan
ÇAKALLIOĞ
LU, 2008
0,617
Based on Science Teaching of
Project-Based Learning Approach
Effect to Academic Achievement and
Attitudes
Master
Thesis
Adana
7th Grade
By the
researcher
Physics