Examining Two Middle School Mathematics Teachers’ Knowledge for Teaching Manipulation of Algebraic Expressions during Lesson Planning and Instruction

Abstract

Teachers use their content and pedagogical content knowledge for teaching algebra. For this reason, the examination of how teachers use this knowledge may help shed light on how students learn algebra, especially in determining why they usually have difficulties. The aim of the current study is to reveal what teachers know, and propose what they actually need to know for teaching the simplification and equivalence of algebraic expressions. The multiple-case study design was used for this study to compare and contrast the two middle school teachers" lesson planning and instruction. The data corpus included lesson plans, actual instruction records, and post-observation interviews. Data analysis was conducted using the Mathematical Knowledge for Teaching (MKT) model. The findings indicated that both teachers had a lack of specialized content knowledge about mathematical representations such as algebra tiles. They did not use algebra tiles effectively and could not link algebraic and geometric representations that underlie the idea of multiplication. It was observed that both teachers generally used unknowns and variables interchangeably indicating the inadequacy of their common content knowledge. In the planning process, the two teachers were able to state the common misconceptions that the students generally had and the ways of addressing them. Through the cases of these two teachers, it was observed that teachers need to have a good conceptual mathematical understanding and also knowledge of students" thinking in order to design effective lessons. Based on the findings, the types of knowledge that the teachers need to have are outlined and the theoretical and practical implications of the study are discussed.

Full text

Turkish Journal of Computer and Mathematics Education Vol.10 No.3 (2019), 588-616
Correspondance: Dilek Girit Yildiz email: dilekgirit@gmail.com
Citation information: Girit-Yildiz, D. & Akyüz, D. (2019). Examining two middle school mathematics teachers‟ knowledge for
teaching manipulation of algebraic expressions during lesson planning and instruction. Turkish Journal of Computer and
Mathematics Education, 10(3), 588-616.
Research Article
Examining Two Middle School Mathematics Teachers’ Knowledge for
Teaching Manipulation of Algebraic Expressions during Lesson
Planning and Instruction
Dilek Girit Yildiz
a and Didem Akyüz
b
aTrakya University, Faculty of Education, Tekirdağ/Turkey (ORCID: 0000-0003-3406-075X)
bMiddle East TechnicalUniversity, Faculty of Education, Ankara/Turkey (ORCID: 0000-0003-3892-8077)
Article History: Received: 24 November 2018; Accepted: 15 July 2019; Published online: 14 November 2019
Abstract: Teachers use their content and pedagogical content knowledge for teaching algebra. For this reason,
the examination of how teachers use this knowledge may help shed light on how students learn algebra,
especially in determining why they usually have difficulties. The aim of the current study is to reveal what
teachers know, and propose what they actually need to know for teaching the simplification and equivalence of
algebraic expressions. The multiple-case study design was used for this study to compare and contrast the two
middle school teachers‟ lesson planning and instruction. The data corpus included lesson plans, actual instruction
records, and post-observation interviews. Data analysis was conducted using the Mathematical Knowledge for
Teaching (MKT) model. The findings indicated that both teachers had a lack of specialized content knowledge
about mathematical representations such as algebra tiles. They did not use algebra tiles effectively and could not
link algebraic and geometric representations that underlie the idea of multiplication. It was observed that both
teachers generally used unknowns and variables interchangeably indicating the inadequacy of their common
content knowledge. In the planning process, the two teachers were able to state the common misconceptions that
the students generally had and the ways of addressing them. Through the cases of these two teachers, it was
observed that teachers need to have a good conceptual mathematical understanding and also knowledge of
students‟ thinking in order to design effective lessons. Based on the findings, the types of knowledge that the
teachers need to have are outlined and the theoretical and practical implications of the study are discussed.
Keywords: Equivalence of algebraic expressions, mathematical knowledge for teaching, simplification of
algebraic expressions, middle school mathematics teacher
DOI: 10.16949/turkbilmat.487243
1. Introduction
Teacher knowledge is an important component of teaching and plays a key role in
students‟ learning. It has been shown that the teacher‟s content knowledge and pedagogical
content knowledge of mathematics has a positive effect on students‟ mathematics
achievement (Hill, Rowan, & Ball, 2005). Especially, mathematics teachers‟ knowledge is
essential to students‟ mathematics achievement (Blömeke & Delaney, 2012). One of the
mathematics learning areas where students generally have difficulty in middle and high
school is algebra (Kieran, 2007). It is important to support students‟ ability to think
algebraically in the elementary grades in order to help middle and high school students from
not experiencing difficulties in algebra (Cai, Ng, & Moyer, 2011). More specifically, the
studies about learning algebra in the early grades show that students generally have

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difficulty in manipulating algebraic expressions (e.g., Banerjee & Subramaniam, 2012;
Booth, 1988; Gunnarsson, Sönnerhed, & Hernell, 2016; Livneh & Linchevski, 2007;
MacGregor & Stacey, 1997; Seng, 2010). Gallardo (2000) asserts that there is a didactic cut
in the child‟s thought in the transition from arithmetic to algebra and that students have a
resistance to operating with unknowns in the transition to algebraic thinking.
Kaput (2000) advocated teaching algebra in the early grades (6 to 12 years of age) and
emphasized the importance of learning “the study of functions, relations, and joint
variation” (p. 19). In connection with this description, two important concepts are variables
and algebraic expressions (Subramaniam & Banerjee, 2004). The development of these
concepts is conceptually and procedurally important in forming an equation and solving it
in later grades. The concept of variable is taught first in the context of generalization of
patterns; then, algebraic expressions are taught conceptually and procedurally in the context
of operations with algebraic expressions in relation to these generalizations (Capraro &
Joffrion, 2006). According to Kieran‟s (2007) model of algebraic activity, the
generalization of patterns is a generalization activity. After this, the transformational
activity comes which requires manipulating the symbolic form of an algebraic expression or
an equation. The scope of this study hence involves the manipulation of algebraic
expressions, which include adding, subtracting, and multiplying algebraic expressions.
Simplification of algebraic expressions involves the collection of like terms, and
equivalence of expressions involves the application of the distributive property in
multiplying expressions. Teachers play an important role in teaching algebra since they are
the ones who make decisions about algebra instruction (Malara & Navarra, 2009). For this
reason, the examination of the teachers‟ methods in teaching and the use of algebra
knowledge in practice may shed light on understanding how students learn algebra in the
transition from arithmetic to algebra and to determine why they usually have difficulty
learning it. Thus, the aim of this paper is to determine teachers‟ algebra knowledge in
teaching operations with algebraic expressions in middle grades. This paper seeks to
address the following question: What is the nature of middle school mathematics teachers‟
mathematical knowledge for teaching the simplification and equivalence of algebraic
expressions in lesson planning and instruction?
1.1. Conceptual frame of teacher knowledge
Teacher‟s knowledge as a term was first defined and used by Shulman (1986); since
then, many researchers have identified the components of teacher knowledge and elaborated
on this concept (Graeber & Tirosh, 2008). In fact, it has been shown that content knowledge
is more effective in teaching when combined with pedagogical knowledge (Ball, Thames, &
Phelps, 2008; Hill et al., 2005). Researchers in mathematics education also proposed
models for teacher knowledge, especially in mathematics based on the frameworks of
teacher knowledge (Cochran, DeRuiter, & King 1993; Grossman, 1990; Shulman, 1986).
There are different components which emphasized by the developers in these frameworks.
In one of the frameworks, Fennema and Franke (1992) emphasized the use of real-life

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situations and manipulatives to promote students‟ understanding. Additionally, Rowland,
Huckstep, and Thwaites (2005) proposed a contingency category which concerns the
teachers‟ knowledge of handling unexpected situations which occur during teaching. There
are also models specific to mathematics teachers‟ pedagogical content knowledge (PCK)
(An, Kulm & Wu, 2004; Chick, Baker, Pham, & Cheng, 2006).
Broader and more detailed than these models, Ball et al. (2008) developed the mathematical
knowledge for teaching (MKT) model. Ball et al. (2008) describe MKT as “the
mathematical knowledge needed to carry out the work of teaching” (p. 395). Ball et al.
(2008) analyzed teachers‟ practices and determined the mathematical demands of teaching
in the development of their model. This model is a domain map which shows mathematical
knowledge for teaching consisting of subject matter knowledge (SMK) and PCK (see
Figure 1). SMK has common content knowledge (CCK) and specialized content knowledge
(SCK) components. CCK is “mathematical knowledge that is used in teaching, but not
directly taught to students” and it is used by people working with mathematics; SCK is
specific to mathematics teachers (Hill, Sleep, Lewis, & Ball, 2007, p. 132). According to
Ball et al. (2008), PCK consists of knowledge of content and students (KCS), knowledge of
content and teaching (KCT), and knowledge of content and curriculum (KCC). KCS is
defined as “the knowledge that combines knowing about students and knowing about
mathematics” (Ball et al., 2008, p. 401). Teachers must be aware of students‟ common
conceptions and misconceptions, errors, and difficulties specific to a mathematical topic.
KCS is a component of Shulman‟s PCK concept; it is apart from subject matter knowledge.
The second subdomain of PCK is KCT. It is defined as “the knowledge that combines
knowing about teaching and knowing about mathematics” (Ball et al., 2008, p. 401).
Teachers need to know how to design instruction for teaching mathematics, lead a
discussion, and make decisions about the instruction. The third subdomain of PCK is KCC.
It is explained as the knowledge of the contents regarding the curriculum order, suggested
activities, and important explanations for teaching.
Figure 1. Mathematical Knowledge for Teaching Model (Ball et al., 2008)
Besides examining teacher knowledge in practice phase, the lesson imaging before the
instruction is also important (Stephan, Pugalee, Cline, & Cline, 2017). The researchers
suggested that the teachers should explain the objective, design the task and how to carry it
out, anticipate misconceptions, design the strategies and their order, prepare questions and
determine how to be aware of students‟ understanding (Stephan et al., 2017). Sullivan et al.
SUBJECT MATTER KNOWLEDGE (SMK)
Common Content Knowledge (CCK)
Specialized Content Knowledge (SCK)
Horizon Content Knowledge (HCK)
PEDAGOGICAL CONTENT
KNOWLEDGE (PCK)
Knowledge of Content and Student (KCS)
Knowledge of Content and Teaching (KCT)
Knowledge of Content and Curriculum (KCC)

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(2015) also added consolidating tasks which provide the connection with prior learning and
supplementary tasks which provide easier or more difficult according to the need of the
students. These researchers take teacher knowledge in planning into consideration and thus
the current study also examined it by combining lesson planning and instruction.
Researchers have also attempted to explain teacher knowledge for particular
mathematical topics, such as algebra (e.g., functions), probability and statistics (Graeber &
Tirosh, 2008). However, there is not much research in the literature about teachers‟
knowledge and practice of algebra (Doerr, 2004; El Mouhayar & Jurdak, 2013; Wilkie,
2014). The studies in the past about teachers‟ SMK generally focused on functions, slopes,
and equations (e.g. Even, 1990; Even, Tirosh & Robinson, 1993; Stump, 1999). More
recent studies focused on both the teachers‟ SMK and PCK for the middle grades and
secondary grade level algebra topics, including inequalities, expressions, and equations
(Artigue, Assude, Grugeon, & Lenfant, 2001; Ferrini-Mundy, McCrory, & Senk, 2006).
Generally, teachers‟ knowledge of students‟ thinking as PCK was examined in the algebra
word problem-solving context (e.g., Nathan & Koedinger, 2000; Van Dooren, Verschaffel,
& Onghena, 2002). As is normally the case, the proposed models and frameworks are
usually about algebra topics at the secondary level (Doerr, 2004). Although there have been
studies about algebra knowledge, Wilkie (2014) has asserted that there are fewer studies
about teachers‟ algebra knowledge as topic-specific in practice in the middle school grades.
Thus, the main issue addressed in this paper is teacher knowledge in teaching manipulation
of algebraic expressions by considering planning and teaching processes together. In
particular, the current research focused on MKT of teachers in the context of manipulation
of algebraic expressions. There are several reasons for using the MKT model in this study.
Teacher knowledge is explained into sub-domains specific to mathematic teaching with this
model (Hill, Ball, & Schilling, 2008). Thus, it is considered to reveal existing teacher
knowledge as specific to manipulation of algebraic expressions, which gives detailed
descriptions of the knowledge domains. Another reason for using this model was that it was
based on observations of teachers‟ instructions as qualitative aspect of the development of
it. Since the main data of this study was observations of the instructions, the MKT model
was found as appropriate. Considering the aims of the study under these contributions, since
MKT model includes content knowledge and pedagogical content knowledge together, it
was preferred to be used for this research.
1.2. Teachers’ knowledge of algebraic expressions
There have been many discussions about teachers‟ knowledge and how it is related to
teaching algebra. Some studies (e.g. Livy & Downton, 2018; Stephens, 2008; Sullivan,
2018; Tchoshanov, Quinones, Shakirova, Ibragimova, & Shakirova, 2017) suggest that pre-
service teachers need to have conceptual knowledge for teaching algebra. Teachers need to
have knowledge of using multiple representations, justifying reasoning, using
generalization and posing problems for teaching algebraic reasoning (Bair & Rich, 2011).
These requirements are about teachers‟ specialized content knowledge (SCK) of algebra

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and it is important to note that transferring SCK to practice is essential for effective
teaching in early algebra topics such as the associative property (Ding & Heffernan, 2018).
However, Huang and Kulm (2012) showed that pre-service teachers did not manipulate
algebraic expressions fluently in functions as CCK requirement. In more detail, pre-service
teachers had difficulty with using representations and examples, and deep questions and so
the content of teacher training programs can be discussed in order to support the teacher
candidates‟ content knowledge of algebra with pedagogy (Ding & Heffernan, 2018).
As well as pre-service teachers, in-service teachers can also have problems in teaching
algebra. Tirosh, Even, and Robinson (1998) examined PCK in the context of algebraic
expressions. They examined teachers‟ awareness of the students‟ tendency to conjoin or
“finish” open expressions, as this tendency caused difficulty in learning algebraic
expressions and operations associated with them. Students with this tendency can add 4x+5
as 9 or 9x, as an example. The researchers studied two novices and two expert seventh
grade teachers, so categorized based on their years of teaching experience. Tirosh et al.
(1998) found that the two novice teachers were not aware of this tendency, while the two
experienced teachers expected that students had this tendency in dealing with algebraic
expressions. The researchers observed that one novice teacher was unaware of the
misconception that students could have; thus, he emphasized adding the numbers and letters
separately, as a rule when teaching simplification of algebraic expressions, and the students
gave incorrect answers. On the other hand, the other novice teacher used rules, adding “like
terms” indicating the terms which had x as like terms. She used fruit salad techniques while
explaining operations in algebraic expressions by representing apples and pears for
variables. However, the researchers observed that these strategies caused some confusion in
student learning. One of the experienced teachers first explained what like terms and unlike
terms were considering students‟ difficulties and continued the lesson using this concept.
The other experienced teacher provided students with conceptualization by using
challenging strategies, such as substitution, the order of operations, and going backward.
Tirosh et al. (1998) suggested that teachers should know the students‟ difficulties and
design their lessons using different approaches regarding the students‟ conceptions.
The knowledge of how students learn, and where students have difficulty are important
elements of pedagogical content knowledge. In this context, Hallagan (2004) developed
tasks which included modeling equivalent expressions, and the teacher implemented the
tasks and constructed a library selecting students‟ different solutions. For example, students
worked on showing and explaining that the 4s+4 expression was equal to 4(s+1),
s+s+s+s+4, 2s+2(s+2), and 4(s+2)-4 in different pictures. This task aimed to determine the
perimeter of a square pool. As a result, the teacher recognized the value of using visual
strategies based on area model to improve students‟ conceptual understanding rather than
using only the distributive property as a procedure. Hallagan (2004) suggests developing a
library which includes samples of students‟ works to enhance teachers‟ knowledge and
improve algebra instruction.

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One of the components of teacher knowledge is knowing students‟ misconceptions as
well as conceptions. Lucariello, Tine, and Ganley (2014) emphasized the importance of
teacher‟s instruction that provides conceptual change about variable concept in algebraic
expressions in order to overcome students‟ misconceptions about variable. They developed
a diagnostic test to determine students‟ misconceptions to guide teachers on how they could
handle the misconceptions before and after the instruction. They pointed out “variable is a
label” and “a specific unknown” misconceptions that the students often have. When a
variable is thought as a label, students could think the variable is standing for an object not
the number of it. This misconception as reversal error is also related to multiplicative
comparison in equality (Weinberg, Dresen, & Slater, 2016). For example, the well known
“students and professors” problem is “there are six times as many students as professors”.
The students could answer incorrectly as 6S=P considering S is a label rather than the
number of students. The teachers should use multiplicative comparison problems to develop
students‟ semiotic language and to support their understanding of the meaning of algebraic
expressions (Weinberg et al., 2016).
Most of the studies in current research literature have examined algebraic expressions
within other algebra topics such as equations, patterns or functions (e.g. El Mouhayar &
Jurdak, 2013; Even, 1990; Even et al., 1993; Ferrini-Mundy et al., 2006; Wilkie, 2014).
Therefore, there is not much research about teachers‟ knowledge of manipulation of
algebraic expressions as topic-specific knowledge and at middle school level (10-13 years).
The current study aimed to make up for this lack in this area by examining algebraic
expressions specifically. This study also goes a step further and examined teacher
knowledge both in planning and teaching. This is important to reveal the teacher‟s role to
support students‟ algebraic reasoning (Blanton & Kaput, 2005; Carraher, Schliemann,
Brizuela, & Earnest, 2006). At that point, this study may contribute to the literature on
algebra teaching and learning. Under this consideration, this paper seeks to address the
following question: What is the nature of middle school mathematics teachers‟
mathematical knowledge for teaching the simplification and equivalence of algebraic
expressions in lesson planning and instruction?
2. Method
2.1. Research design
In this study, the qualitative research design was used to uncover middle school
mathematics teachers' mathematical knowledge for teaching in the context of algebraic
expressions. In order to study teacher knowledge, taking the teaching process into
consideration, qualitative research should be used (Kahan, Cooper, & Bethea, 2003). Case
study approach includes a case/cases that is/are explored by the researcher, detailed and in-
depth data collection from multiple sources (e.g. observations, interviews), and reporting
the themes for the case (Creswell, 2007). Particularly, the multiple-case study design is
preferred for this study to compare and contrast the exemplary outcomes of two teachers‟
instructions (Yin, 2003). The comparison of two cases could provide making an

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interpretation about the knowledge that the teachers should have by emphasizing the
existing and lack of knowledge in two cases. The context is the algebraic expressions. The
cases are two middle school mathematics teachers, and the unit of analysis is teachers‟
mathematical knowledge for teaching in this design.
2.2. Participants
The participants were two middle school mathematics teachers and they work in the
same public school. They were teaching algebra topics to 7th grade students at the same time
during the data collection and thus these teachers were selected and convenient sampling
method was used because of this accessibility. The teachers in this study had a master‟s
degree in elementary mathematics education, and they have also been in a doctorate
program in elementary mathematics education. One of the purposes of the study is to
propose required knowledge types as a conceptual framework, thus the choice of these
teachers can be considered appropriate. The names of the participants were changed for
confidentiality, and code names were used as Ece and Eda to represent them.
2.3. Data collection
The data collection procedure had three phases in this study: pre-instruction, during
instruction, and post-instruction. In the pre-instruction phase, the teachers prepared the
lesson plans individually, and the researcher interviewed each teacher on their lesson plans.
In the second phase, during instruction, the researcher observed the lessons in two different
7th grade classes, took field notes, and video-recorded. After each class session, the
researcher conducted post-observation interviews with the teachers (see Figure 2).
Figure 2. The process of data collection
The data collection process took about 24 class-hours (1 class-hour was 40 minutes),
which included the total of two teachers‟ instructions. While the planning provided an
understanding of the teachers‟ existing knowledge, the instruction provided an observation
on how the teachers used their knowledge while teaching. The teachers prepared the lesson
plans with the following objectives: “Add and subtract algebraic expressions, multiply a
whole number and an algebraic expression, and multiply two algebraic expressions”. The
purpose of the post-observation interviews was to check whether the researcher understood
Lesson planning
•The teachers
prepared the lesson
plans individually
•Individual
interviews were
made with each
teacher on their
lesson plans.
Practice
•The teachers
implemented their
plans
•The researcher
observed them and
took notes
Post-observation
interviews
• The researcher
interviewed with
the teachers
individually after
each lesson

Examining Two Middle School Mathematics Teachers’ Knowledge for Teaching Manip…
595
the teacher‟s instruction properly by observing the lessons by comparing the teachers'
responses. Thus, the data collection process of this study could give a holistic understanding
of teaching with planning and instructions.
2.4. Data analysis
The analysis of the qualitative data begins by forming an initial and tentative coding and
then continues with grouping them in themes with respect to similarities and ends with
reporting the findings (Merriam, 2009). For this study, the cases as the two teachers‟
planning and instructions were analyzed and described independently first. The data from
the cases were analyzed and coded as a statement, an explanation, a dialogue, or a question
that was considered a meaningful unit. Then, the extracted codes were put into one of the
themes and then sub-themes considering the descriptions and definitions of themes and sub-
themes in the MKT model.
In the analysis, SMK and PCK as knowledge domains were considered as themes and
their components as knowledge sub-domains (CCK, SCK, KCS, KCT, and KCC) were
considered as sub-themes for this study. This categorization provided an analysis of cases
individually within itself. Yin (2003) suggested cross-case synthesis as an analytic
technique for the analysis of two or more cases. The researcher can compare and contrast
the cases based on the framework that is used for analysis. Thus, after forming these
tentative codes, the codes which were categorized by comparing and contrasting and had a
pattern in one case were also analyzed for the other case. From the analysis of two cases,
the codes which occurred in the two cases within a pattern were determined for the current
study. To ensure the reliability of the research, the data were coded separately by the
researchers. Then the researchers came together to evaluate their coding and then reached a
full agreement with discussing the coding. Besides, in this study, data were collected from
several sources that were preparing lesson plans, interviews, and observations in order to
provide trustworthiness.
3. Findings
In this section, the MKT of Teacher Ece and Teacher Eda are presented according to
their lesson plans they prepared on the topic of algebraic expressions, the observations of
the lessons they taught and interviews after each lesson.
3.1. Teachers’ lesson planning
Ece designed the instruction of addition and subtraction with algebraic expressions by
beginning with the questions in the textbook (Aydın & Gündoğdu, 2016, p. 187) that had
contexts requiring representation of given information algebraically and then carrying out
the operations. One of the questions was like this:
Question: There are 2 eggs and 4 olives in one of the plates, and there are 1 egg
and 6 olives in the other plate. In total;
How many eggs are there?

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How many olives are there?
Can you add olives and eggs?
Can you subtract eggs from olives?
Ece planned to ask the students to represent the number of eggs and olives algebraically
and then how like terms were added when the eggs and olives were gathered. To illustrate,
their addition was represented as 2y+4z (y represented egg, z represented olive). However,
the number of eggs and olives are known, thus it would be troublesome to represent the
known situations with algebra concepts. After solving these questions, she planned to model
addition and subtraction operations by using algebra tiles. The first example to model with
algebra tiles was (3x-2)+(2x+6) in her lesson plan. While modeling, she planned to
represent the expressions separately first using the tiles as in the following figure:
Figure 3. The representation of x, +1, and -1 with tiles in Ece‟s lesson plan
She explained the implementation of the modeling in planning. She indicated grouping
the variables (3x and 2x), and constant terms (-2 and +6) separately and then adding these
expressions in order to get the result as 5x+4 in her lesson plan.
On the other hand, Eda designed the instruction of addition and subtraction with
algebraic expressions by beginning properties of operations. She planned to show these
representations in the table that included the arithmetical operations and the corresponding
operations with algebraic expressions. This table included the arithmetical operations in the
first column, the algebraic representations of it in the second column, the terms in the third
column, and the coefficients in the fourth column as exemplified for the first row as in the
following table:
Table 1. Operations and their algebraic representations
3+2.3=3.3
x+2x=3x
x, 2x, 3x
1, 2, 3
Eda planned to begin with this matching activity and then, she planned to define like
term concept as in the textbook.
For the instruction of multiplication with algebraic expressions, Ece planned to begin
with Nermin’s Money Activity in the textbook (Aydın & Gündoğdu, 2016, p. 193). It was
required to write algebraic expressions of verbal statements and the multiplication of a
number and an algebraic expression. This activity was like in the following:
Nermin saves money from her allowance and has some in her moneybox. Nermin
puts 5TL that her mother gave into her moneybox. Her father said that he would
give her money twice as much as the saved money. Write the algebraic expression
that Nermin would take from her father and explain how you would write it.

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Then, she planned to model multiplication operation by using algebra tiles. When she
was asked how the tiles could provide the students to link to multiplication idea, she
explained like this:
Ece: I will make these tiles by myself or I will want the students to prepare them.
They can make by using colorful papers. These tiles modeled the multiplication of
algebraic expressions. For example, 4x, suppose this represents
“x”. How many x are there? Let‟s add. We put four of them side by side. Then, I
connect like this; the shortcut is 4.x of this addition operation. We can do like this.
Figure 4. The representation of 4x with algebra tiles
Ece explained that the algebra tiles would provide the demonstration of the repeated
addition by putting 4 tiles side by side. She planned to link the representations for
multiplication operation by using algebra tiles in this way. However, she did not indicate
the concept of area calculation in this representation to link algebraic and geometric
representations since her knowledge to choose, make and use the algebra tiles did not seem
to support this. Focusing on repeated addition in this representation could not have provided
this link to underlie the multiplication idea. She also expressed her concerns and
anticipations about students‟ difficulties in applying the distributive property in
multiplication and modeling with algebra tiles for multiplication:
Ece: The students can understand easily addition and subtraction by modeling with
tiles. Since they see similar ones and add them to find their number. But, they have
difficulty with the multiplication, especially while using distributive property such
as 2.(3x+2). The students can confuse addition with multiplication. Perhaps, they
can understand it by modeling with tiles. But they have difficulty using the tiles,
also.
On the other hand, for the multiplication of algebraic expressions, Eda too planned to
use algebra tiles. She planned to make links among algebraic and geometrical
representations to give the idea of multiplication of algebraic expressions:
Eda: For multiplication, I will use algebra tiles, if there are, or I will prepare with
papers, or I will draw on the board. The students can understand while using the
area of a square because they know the area of a square well. They also can use

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the area of rectangle easily. The length of the sides is x and x, the area of this
square is x2. When x+3 is asked, 3 units are added. They can connect the
multiplication with the area concept with this activity.
After teaching multiplication with modeling, she planned to apply the distributive
property for multiplying algebraic expressions procedurally. Therewith, when the
researcher asked students might have what possible misconceptions on this topic, the
teacher explained the misconceptions in addition and subtraction of algebraic expressions
by giving examples as follows:
Eda: For example, in 3x-x, the students can forget 1 as the coefficient of x. They
have difficulty; they cannot understand this 1 easily. ... Another example is 4x+3y-
x. They can add or subtract all the coefficients without considering whether the
variables are the same or not.
She also pointed out the common misconceptions in multiplication:
Eda: When x is multiplied by x, the students can get 2x. Higher achieving students
do not make this error. Other students are generally confused about this. They
know the result is x2 from the area of a square. However, they make errors.
Especially, if there is a coefficient of x, such as 2x. Multiplication of 2x and x.
They are more likely to make this error.
In sum, for teaching simplification of algebraic expressions, Ece‟s knowledge to choose
which examples to start with was inappropriate since the questions were problematic for
using variables. On the other hand, Eda‟s knowledge to choose which examples to start
teaching addition and subtraction appeared efficient with connecting the properties of
arithmetical operations that the students had learned before. However, her knowledge to
choose which examples to take the students deeper into the content appeared limited
because of focusing on the properties of operations, merely not just the like term. For
teaching multiplication, Ece‟s knowledge of sequence activities was appropriate. The
sequence for teaching multiplication of algebraic expressions included first connecting
multiplication concept with real-life situations, then connecting repeated addition with
multiplication, and than using models to show how the algebraic expressions were
multiplied. However, she did not emphasize the area concept underlying modeling in using
algebra tiles. On the other hand, Eda planned to use algebra tiles with modeling in
multiplication (KCT).
Ece‟s knowledge to choose, make and use the algebra tiles as representation was
appeared inadequately since focusing on repeated addition in using of algebra tiles could
not have provided the link among algebraic and geometric representation that underlie the
multiplication idea. On the other hand, Eda‟s knowledge to link algebraic and geometrical
representations underlying the area concept and of how to choose, make, and use
mathematical representations was appropriate. She explained the area concept that underly
modeling multiplication of algebraic expressions with algebra tiles correctly (SCK).

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3.2. Types of knowledge in instruction
3.2.1. Teachers’ common content knowledge (CCK) of algebraic expressions
This study revealed that the teachers' common content knowledge included mostly the
knowledge of the definition of the terms, and solving or answering the questions related to
algebraic expressions. Ece‟s knowledge of the constant term concept was incorrect as she
did not accept it as a term in an algebraic expression. To illustrate, Ece did not take the
constant term as a term and answered the questions incorrectly as explained in the following
script:
Ece: a2-3a-4+2a+5a2, how many terms are there? Is „a2‟ a term? Yes. Is „-3a‟ a
term? Yes. Is „-4‟ a term?
Students: No.
Ece: What is it? It is a constant term, not the term. 2a is a term, 5a2 is a term. How
many terms are there? 4.
In this situation, Ece explained that -4 was not a term since it was a constant term. She
knew that -4 was a constant term but she did not accept it as a term, so her knowledge to
use the terms appeared incorrect. It showed her lack of content knowledge about term
concept in the algebraic expression. In the post-interview, the dialogue about constant term
was as follows:
Researcher: You did not accept the constant as a term.
Ece: Is it a term?
Researcher: The constant term is also a term.
Ece: So, we take it as a term?
Researcher: Yes, the term is described as the part that is divided by a plus or minus
sign. You can examine like this. The constant is a special situation.
Ece: It is also a term. That‟s right.
On the other hand, Eda's knowledge to use the term, like term, the constant term, and
coefficient concepts appeared to be well developed. She made explanations about algebraic
expression and emphasized the like term concept and gave several examples in the
instruction as below:
Eda: When an algebraic expression is told, the concept of the term comes to the
mind. Let‟s look at 2x-3y+5. The terms are considered with their signs. Here, the
terms are 2x, -3y, +5. Thus, if how many terms there are is asked, look at the parts
which are divided by + and – signs. Here, there are 3 terms. The coefficient is the
other concept. We call the coefficient as the number which is multiplied by the
unknown in each term. The coefficient of x is 2 (2x), and the coefficient of y is -3.
Be careful! We take it as minus with its sign. We call the constant term as the term
which is not multiplied by any unknowns.

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Another situation that could be problematic for the two teachers was that they used the
unknown and variable concept as if they had the same meaning. To illustrate, Ece used two
examples: 8t+3 and -9x-7. She explained that 8 and -9 were the coefficients; t and x were
the unknowns; 3 and 7 were the constant terms; and 8t and -9x were the terms. She used the
unknown and variable concept together as they had the same meaning since she wrote
“variable/unknown”. Eda also used these concepts similar to Ece. The teachers did not
differentiate between them because their knowledge of these terms was inadequate.
In general, Eda solved the questions and problems correctly with adequate explanations;
however, Ece could not solve or answer the questions related to algebraic expressions
correctly since she ignored what was given or asked several times during the instruction.
Ece answered what she found instead of what was asked in the question. To illustrate, she
found 2n+10 correctly by multiplying 5 and (n+2) but she incorrectly expressed what it
referred to. She expressed 2n+10 as the total money in the money box, but she should have
added 2n+10 and n+5, and got 3n+15 for total. Another example was that she did not
simplify 3(X+Y)+3(Y+7Z) expression and thus she indicated that it did not match with any
expressions in options equally. In other words, she missed some points, thus she did not
answer the other questions in planning correctly and completely.
3.2. Teachers’ specialized content knowledge (SCK) of algebraic expressions
This study revealed that the two middle school mathematics teachers‟ specialized
content knowledge included mostly the knowledge to use representation, to provide
mathematical explanations, and to use the mathematical language. Although Ece did not
correct the students‟ incorrect use of the equal sign or determining the term without the
sign, she used the notations appropriately by herself in the instruction of operations with
algebraic expressions. For example, in simplifying (2x+1)2+5x, a student first multiplied
2x+1 by 2 and then wrote 5x next to the result of the multiplication and he used the equal
sign inappropriately as shown in Figure 5.
Figure 5. The use of equal sign by a student
In this situation, Ece did not correct this representation, and regarded the result as
correct and explained this student‟s solution to the class, so her knowledge of how
mathematical language was used appeared inappropriate. In contrast to this, Eda corrected
the errors in the use of the equal sign appropriately and explained and corrected the
students‟ incorrect writings. When the students collected the like terms separately in

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another place and they did not write them as a result as in Figure 6, Eda corrected and wrote
them as the result in the right side of the equal sign.
Figure 6. The writing for the simplification of 3x-4y+2x-y
Eda also represented the kind of variable with apple and pear analogy, and the
procedures with net worth concept by using asset-debt concepts properly in order to teach
addition and subtraction. To illustrate, she made explanations for the simplification of
3x+4a-5x-2a+7 as in the following script:
Eda: Let‟s examine this example: 3x+4a-5x-2a+7. Which of them are like?
Student: 3x and 5x … one more, 4a and 2a.
Eda: What is 7?
Student: The constant term.
Eda: Then, you have 3 (3x) apples and you are told to give 5 apples to someone.
Can you give?
Students: No.
Eda: What then? You owe 2 apples. That‟s -2x. Then, I have 4 pears (4a), and you
are told to give 2 pears to someone.
Student: +2a is left.
Eda: -2x+2a. There is 7 but there is nothing to add with it. The result is -2x+2a+7.
The students could find the like terms as 3x and 5x, and 4a and 2a. Eda asked the
students to add them by representing apples for x and pears for a, and net worth for
operations. In this example, her knowledge of mathematical language use by expressing the
procedures with net worth concept through using assets and debts concepts as analogy
appeared appropriate. Actually, she had stated to use rectangular and unit square papers to
represent the variables in the lesson planning, but she did not use them in the instruction.
Instead of this, she used apple-pear analogy to represent the kind of variables.
In teaching multiplication of algebraic expressions, the teachers' connection with the
prior topic in order to explain the distributive property of multiplication appeared
appropriate in different ways. Ece connected multiplication with repeated addition to
explaining this property. Ece wanted the students to model 4x as “Is it the long way,
x+x+x+x, to add 4 of x? We have multiplied 4 by x, and that‟s 4.x=4x” (see Figure 7).

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Figure 7. The representation of 4x with algebra tiles
In this situation, Ece represented 4x using the 4 algebra tiles of x as seen in the figure.
She did not make explanations about the meaning of 4x, which was the area of the rectangle
whose sides were 4 and x, and so she did not indicate the area concept. On the other hand,
Eda connected the application of this property with integers appropriately. However, the
teachers‟ conceptions about algebra tiles appeared different and inadequate. While Ece used
the tiles focusing on repeated addition by counting the number of tiles, Eda did not use
them in her instruction though she emphasized the importance of using connecting the area
concept in planning. Neither of the teachers used algebra tiles effectively and linked
algebraic and geometric representation to underlie the multiplication idea. Their knowledge
to evaluate the instructional advantages and disadvantages of algebra tiles as representations
were inadequate in the post interviews.
In the multiplication of two algebraic expressions, Ece did not provide adequate
mathematical expressions. To illustrate, some students had difficulty in the
conceptualization of n2 in the multiplication of 2n by 3n. Ece asked a student to explain
why the result was n2 and approved his explanation. The students said that “Because there
are two „n‟s.” In this situation, the student‟s answer was acceptable since he could think that
there were two n‟s multiplied. However, Ece's response to the student was not adequate as a
mathematical explanation since the existence of two items does not always yield n2. To
illustrate, n+n expression had two items of n and yielded 2n. Thus, her knowledge of how
mathematical language was used appeared inappropriate. Instead of this, the teacher might
have stated that there were 2 multiplied items of n.
3.3. Teachers’ knowledge of content and students (KCS) in algebraic expressions
This study revealed that the two middle school mathematics teachers‟ knowledge of
content and students included mostly the knowledge to anticipate where and how the
students have difficulty and possible misunderstandings. Generally, Ece‟s knowledge to
anticipate the misunderstandings that might arise while studying like terms were inadequate
since she emphasized only the kind of variable without considering its power. She
explained the like term concept stating that it had the same variables with same or different
coefficients; however, this definition was inadequate as x and x2 were the expressions that

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had the same variable but they were unlike terms and the definition could cause
misconceptions. Ece did not show the signs of the constant term while determining it,
either. On the other hand, Eda explained the like term concept, the procedures of the
addition operation, and the sign before the parenthesis adequately with her knowledge of
understanding the difficulties of students and considering the needs of the students. For
example, she indicated the requirement of the same variable and power for like term as in
the script:
Eda: …The terms whose variables and powers are same are like terms. For
example, 3x and - 5x. Are they like, a2 and 4a2?
Students: Yes.
Eda: 3x2 and 3y2?
Students: They are not.
Eda: Yes, look at the variables. 4x2 and 4x? Are they like terms?
Student: They are not because one of them does not have a power.
In the planning process, the teachers had stated common misconceptions that the
students could have based on their previous experiences such as the students‟ thinking of
4.x as a two-digit number, or x.x as 2x, or ignoring 1 as the coefficient of x in 3x-x, or
adding unlike terms. The teachers also noticed these misconceptions in the instructions.
In Ece‟s class, the students added unlike terms. To illustrate, in finding a+b when
a=(2x-1), b=3(x+3), a student did operations as in the following script:
Student: Since there is not a distribution in a, I am writing 2x-1=1 (The teacher
corrected it, then the student is distributing 3 to (x+3) for b as in Figure 8)
Ece: Have you found 12x from adding 3x and 9? Are they like terms? (The student
is writing 3x+9). Add 2x-1 and 3x+9.
Figure 8. The misconception related to adding unlike terms
In this situation, the student explained 2x-1=1 incorrectly. However, 2x and -1 were not
like terms and thus they could not be added or subtracted. Ece did not make any
explanations about the fact that these terms were not the like terms, and she only erased 1.
Then, the student used the distributive property for b, and he found 3x and 9, added them
and found 12x, which was incorrect. Ece asked the student to add 2x-1 and 3x+9. Although

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some students, as it is seen, could not conceptualize the like term concepts for addition and
subtraction, Ece did not provide any explanations again. Her knowledge of how to address
the student‟s errors and correct them appeared inadequate. Since she realized the student‟s
errors during instruction, she only corrected them herself, but she did not ensure if the
errors were corrected and if the students learned the concepts conceptually. Another
example was related to ignoring coefficient „1‟ of the variable in Eda‟s class as in the
following script:
Eda: What are the terms in a-2b+7?
Student: 2 and 7.
Eda: The terms? Each of them is a term here: a, -2b, and 7 … What are the
coefficients?
Student: -2 and 7.
Eda: Are you sure?
Student: There is 1 in a.
Eda: How many „a‟s are there in this expression? 1. The other coefficients: 1 and -
2. It does not matter whether it is a or x. If there is one variable, the coefficient of
it is 1.
In this situation, Eda corrected the students‟ answers while they were determining the
terms. The students could not consider that the coefficient of the variables was 1 if there is
no number in front of it. Eda explained that there was one „a‟ in the expression and so the
coefficient of it was 1. Her knowledge to address the students‟ errors and to correct them
appeared effective in her explanation while doing this exercise.
Last, in the instruction of multiplication of algebraic expressions, Eda especially
emphasized the difference between area and perimeter concepts. Her knowledge to
anticipate the misunderstandings that might arise while studying these concepts in solving
problems related to geometry was appeared.
3.4. Teachers’ knowledge of content and teaching (KCT) of algebraic expressions
This study revealed that the two middle school mathematics teachers‟ knowledge of
content and teaching included mostly choosing examples to start and take the students
deeper into the content. Generally, the teachers‟ knowledge to choose examples and
activities to start and then to take the students deeper into the topic was appropriate. In the
simplification of algebraic expressions, Ece started with connecting the like term concept
with real-life situations. She used problems related to real-life situations for teaching;
however, her knowledge to choose which examples to use to take the students deeper into
the content was inappropriate as she represented the number of known items with algebraic
representations. To illustrate, she implemented the activity to make the students feel the
need of like terms for addition. This activity had two plates, one of which had 2 eggs and 4
olives, and the other had 1 egg and 6 olives. The teacher drew two plates on the board and
asked how eggs and olives could be added:

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Ece: How can we express the addition of eggs and olives?
Student: 2y+4z.
Ece: That‟s it! You have added eggs and olives separately. It is the same for the
second plate. 1y+6z. Can we not write 1 as the coefficient of y?
Students: Yes.
Ece: y+6z.
Student: Why do we express them as y and z?
Ece: We used the letters to represent egg and olive.
This question enabled the students to think the similar ones could be added. The teacher
used this activity to connect it with the concept of like terms as mathematical ideas.
However, the student answered as 2y+4z, and Ece accepted this answer and the teacher also
expressed the second plate as 1y+6z algebraically. The number of eggs and olives were
known in these plates and thus expressing them algebraically was troublesome. That was,
one student, did not understand why eggs and olives were represented with y and z letters.
Different from Ece, Eda started by connecting the properties of arithmetical operations that
the students had learned before. Then, she emphasized the like term concept by using
different colored unit cubes to take the students deep into addition and subtraction.
In equivalence of algebraic expressions, Ece chose repeated addition to represent
multiplication and used algebra tiles. She asked what (4m-3)+(4m-3) was and a student
added the like terms and got the correct result as 8m-6. Therewith, Ece guided the students
to find the common number in the expression and show as 2(4m-3). She also used the tiles
by indicating repeated addition as explained above. On the other hand, Eda focused on the
application of distributive property by connecting it with integers. She selected these two
similar structures, 3(4-1) and 3(x-1), from arithmetic and algebra to explain the distributive
property for multiplication of algebraic expressions connecting with arithmetic. The
dialogue between Eda and the student is as follows:
Eda: For example, we did 3(4-1). What do we do if there is a number before the
parenthesis? Normally, you do the operations in the parenthesis. Also, we said
another method.
Student: Multiply 3 by 4, and then 3 by -1.
Eda: Okay … If it is 3(x-1), compare the two of them. We write x in the place of 4.
What can we do? We can distribute 3, multiply 3 by x, 3x; 3 by -1, -3. That‟s 3x-3.
Her knowledge of connecting algebraic and arithmetical structure was appropriate. She
explained the distribution procedurally and then used this rule for the next multiplications.
In sum, the teachers have partially adequate knowledge for teaching manipulation of
algebraic expressions. The findings also showed that the knowledge components (CCK,
SCK, KCS, and KCT) are interrelated with each other. Teachers‟ appropriate subject matter
knowledge influenced positively pedagogical content knowledge and how they teach
algebraic expressions.

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4. Conclusion and Discussion
The purpose of this study is to reveal what types of knowledge mathematics teachers
have in lesson planning and how they use them in their practices and to propose what
mathematical knowledge they need for teaching operations with algebraic expressions. In
the following section, these issues are discussed, and the implications and suggestions to
develop teaching with respect to teacher knowledge in practice are presented.
4.1. What do teachers know and what other knowledge types do they need to have to
teach algebraic expressions?
Regarding CCK, the teachers used the unknown and variable concepts as if they had the
same meaning; they did not differentiate between them because their knowledge of these
terms was inadequate. Similarly, Dogbey (2016) noted the teachers' limited understanding
of the use of variables in different contexts. There are different uses of variables in
generalized arithmetic and in solving problems. Variables are generalized numbers in
operations, such as addition and multiplication and the relationship of patterns, while they
are unknowns or constants in solving equations in the problem contexts (Usiskin, 1988).
Regarding SCK, Eda‟s apple-pear analogy was used by one of the novice teachers; this
method was called the fruit salad method in Tirosh et al.‟s (1998) study, and it provided an
explanation of the addition and subtraction of different variables. The teacher in this study
used this analogy when the students had difficulty understanding simplification;
consequently, the students answered the questions correctly. However, Tirosh et al. (1998)
asserted that this method did not provide a relational understanding of operations with
algebraic expressions. However, Ojose (2015) suggested the use of this type of real-life
example, such as apples and oranges, as a model to teach adding unlike terms. Filloy and
Sutherland (1996) found that the use of concrete models, such as tiles or the apple-pear
analogy, helps students‟ transition to the abstract level. In the multiplication of algebraic
expressions, Hallagan (2004) developed tasks to explore the equivalence of expressions
using area modeling such as 4(s+1) and 4s+4. These types of activities were implemented,
and the development of students‟ understanding of equivalent expressions was observed.
However, Ece used algebra tiles for explaining repeated addition in the multiplication of
algebraic expressions. Caglayan (2013) stated that multiplication can be modeled by
repeated addition, but the reasoning of multiplication requires explaining area modeling. On
the other hand, Eda appropriately connected with the application of this property in
integers. This method is also suggested by Ojose (2015) as exemplifying with integers first
and then connecting algebraic expression to help the students‟ learning. While Ece used the
tiles focusing on repeated addition with counting the number of tiles, Eda did not use them
in her instruction, though she emphasized the importance of using algebra tiles for
connecting the area concept in lesson planning. Thus, the two teachers did not use algebra
tiles effectively and did not link algebraic and geometric representation to underlie the
multiplication idea. They used them to provide visuals and concreteness. However,
combining geometrical reasoning with other learning areas is one of the targets of

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mathematics teaching (National Council of Teachers of Mathematics [NCTM], 2000). The
exploration of the multiplication of algebraic expressions by connecting the sum areas of
tiles provides conceptual understanding (Caglayan, 2013). Bair and Rich (2011)
emphasized the importance of using multiple representations to develop teachers‟ SCK.
Regarding KCS, Ece‟s explanation of the like terms concept could cause
misconceptions. As Tirosh et al. (1998) indicated that the novice teacher who explained like
term as having x was not aware of the students‟ misconceptions about adding unlike terms,
and the students had difficulty in simplification of algebraic expressions. In contrast, Eda
emphasized the parentheses in operations considering the difficulties and the needs of the
students. The studies suggest emphasizing the brackets while teaching operations to
elementary level students (Hoch & Dreyfus, 2004; Marchini & Papadopoulos, 2011).
However, it is important to note the understanding of the structural sense of algebraic
expressions by focusing on quantitative relationships as operations and representations
symbolically by using the same and different letters in order to prevent students‟ errors and
improve conceptual understanding (Molina, Rodríguez-Domingo, Cañadas, & Castro,
2017). In the planning process, the teachers also stated common misconceptions which the
students could have based on their previous experiences, such as the students‟ thinking of
4x as a two-digit number, and the teachers encountered these misconceptions which Seng
(2010) identified. In the instruction of multiplication of algebraic expressions, Eda
especially emphasized the difference between area and perimeter concepts. As she stated,
the students can confuse the perimeter and area concepts, and the reason might be their
formulas or representing the same region (Ashlock, 2006).
Regarding KCT, the real-life examples that Ece chose to start simplification of algebraic
expressions were not appropriate because they had known values and could not appropriate
for representing these values algebraically. For teaching multiplication, Ece‟s knowledge of
sequence activities was appropriate. She used a real-life example to start and then used
repeated addition to explain multiplication. However, she could not use algebra tiles
effectively. On the other hand, Eda‟s knowledge to choose which examples to start teaching
addition and subtraction appeared efficiently by connecting the properties of arithmetical
operations that the students had learned before. Eda started by connecting the properties of
arithmetical operations, which was one of the commonly suggested approaches for
connecting arithmetic with algebra (Banerjee & Subramaniam, 2012; Livneh & Linchevski,
2007; Subramaniam & Banerjee, 2004). Molina et al. (2017) also pointed out that the lack
of understanding of the relationships in arithmetic expressions can cause errors in
structuring algebraic expressions. Next, Eda emphasized the like term concept using
different colored unit cubes to take the students deeper into addition and subtraction, as
Filloy and Sutherland (1996) suggested. However, Eda did not use algebra tiles for teaching
multiplication as she indicated in lesson planning.
In addition to the teachers‟ existing knowledge as explained above, this study also
proposed, based on the literature, what types of knowledge teachers need to have to teach
operations with algebraic expressions.

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In addition to KCS, Tirosh et al. (1998) pointed out that the teachers should design
lessons considering the students‟ difficulties. Particularly when teachers instruct
multiplication, it was found that the students generally do not have an adequate
understanding of the structure of expressions, and they have difficulty understanding the
concept of the distributive property (Kieran, 1989). Therefore, the teachers can emphasize
the structure of algebraic expressions in order to support students‟ understanding. Teachers
should also be aware of possible misconceptions that the students could have when they
design lessons. In addition to teachers‟ identified misconceptions, others include incorrect
order of operations, incorrect addition of integers, incorrect multiplication of a negative
integer before the bracket, ignoring the multiplication of the second term in the brackets in
using the distributive property, and incorrectly writing the result of addition of exponential
forms (e.g., 7a2 as 14a) (Seng, 2010). Also, intuition about new notations, misapplication of
rules, operating with negative integers, and inadequate conceptions about the structure of
algebraic expressions can cause the students to encounter difficulties (MacGregor & Stacey,
1997; Seng, 2010). Moreover, Novotná, and Hoch (2008) showed that the lack of structural
sense in high school students prevented them from understanding abstract algebra at the
university. Thus, teachers should have knowledge of these common misconceptions and the
possible reasons for them. For both simplification and multiplication, students‟ reasoning in
algebra could also be an important component of KCS. Lepak, Wernet, and Ayieko (2018)
proposed the concept of students’ reasoning in algebra and defined it as making sense of
context in problems, identifying quantities and relationship between them, representing
them algebraically, executing calculations, and justifying solutions. Teachers should take
into these competences consideration to support students' algebraic reasoning and also
develop their KCS of algebra.
In addition to KCT, teachers can use substitution, the order of operations, and going
backward strategies to teach simplification of algebraic expressions (Hallagan, 2004; Tirosh
et al., 1998). In order to build the students‟ thinking ability, teachers can present the
procedures of operations with algebraic expressions by connecting the arithmetic
procedures based on the similarity of the structure of expressions. This improves the
students‟ understanding of rules and procedures in operations, simplifications of algebraic
expressions, and the equivalence of the expressions (Banerjee & Subramaniam, 2012).
Besides, teachers should use strategies and tasks that would attract students' interest in
combining pedagogical elements of social constructivism in teaching algebra (Prendergast
& O‟Donoghue, 2014).
In addition to KCC, Wilkie (2014) proposed that teachers could evaluate the content
descriptions with scaling. Thus, the knowledge to evaluate objectives, content descriptions,
and sample activities related to the algebra topics in the curriculum could be considered as
KCC which the teachers need to have.
In sum, the MKT which teachers should have for teaching operations with algebraic
expressions can be proposed as in Table 2:

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Table 2. The proposed knowledge types for teaching manipulation of algebraic expressions
Knowledge
types
Description (specific for teaching algebraic expressions)
CCK
The knowledge to use the concepts of the term, like term, constant term, and
coefficient correctly
The knowledge to use the concept of variable and unknown correctly
The knowledge to solve math problems related to operations with algebraic
expressions correctly
SCK
The knowledge to develop or choose the usable definition of the term, like term,
coefficient, constant term, and variable concepts
The knowledge to connect multiplication of algebraic expression with repeated
addition as prior topic / The knowledge to connect the distributive property in
multiplication with the application of it in integers
The knowledge to link algebraic representation to the concept of area to geometric
representation with algebra tiles
The knowledge of how analogies as mathematical language are used for explaining
the kind of variables and the operations
The knowledge of how notations (equal sign and minus sign) are used
The knowledge of how mathematical language is used for explaining the
multiplication of a variable by itself
KCS
The knowledge to anticipate the students‟ difficulty in the application of distributive
property in multiplication
The knowledge to anticipate the misunderstandings that might arise while studying
like term concept
The knowledge of students‟ common misconceptions about the multiplication of a
number and a variable or a variable by itself
The knowledge to understand the difficulties of students in operating with the
parenthesis algebraic expressions
The knowledge of common students‟ misconception about the perimeter and area
concepts of rectangle
KCT
KCT
The knowledge to choose which examples to start teaching addition and subtraction
appeared efficiently by connecting the properties of arithmetical operations
The knowledge to decide when to ask how to collect/simplify terms in classroom
discussion
The knowledge of how to address the students‟ errors in determining like terms and
correct them
The knowledge to evaluate the advantages or disadvantages of using algebra tiles in
teaching multiplication
The knowledge of how to address the possible errors of students in calculating the
area and perimeter of squares or rectangles using algebraic expressions and correct
them
KCC
The knowledge to know and evaluate the content and objectives in the curriculum
related to operations with algebraic expressions

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4.2. Implications and suggestions
One of the most important implications of this study is the proposed knowledge types
specific to operations with algebraic expressions (see Table 2). The proposed knowledge
types can be used to develop algebra knowledge models, and, thus, this study might
contribute to teacher knowledge of algebra. Teacher knowledge can also be examined in
other algebra topics, such as equations, slope, and linear equations, in the middle grades in
order to provide a general overview of the algebra knowledge of teachers. The proposed
knowledge types can also be used to train pre-service and in-service teachers. The courses
in teacher training programs can include the use of specific representations, models,
mathematical language, instructional methods, and teaching techniques to develop teachers‟
knowledge. The school practicum courses can also be designed to develop pre-service
teachers‟ teaching practice, and, therefore, developing teaching practices can enhance pre-
service teachers‟ specialized content knowledge (Aslan-Tutak & Ertaş, 2013).
Other implications include the necessity of developing teachers‟ knowledge of using
particular representations or materials and the teachers‟ knowledge of students‟ thinking, as
essential elements for the effective teaching of mathematics. To support in-service teachers,
meetings can be conducted where the teachers come together and share examples and
experiences from their classes, ask for suggestions about what they can do, and note where
they have difficulty in their teaching. Mathematics education researchers can also inform
the teachers about the results of their studies and suggest activities or examples and
methods from the literature for these training sessions.
There might also be different knowledge descriptions within different contexts, such as
numbers or geometry. However, Horizon Content Knowledge (HCK) (Ball et al., 2008) for
teaching algebra topics was not observed in the current study. Therefore, future research
should also concentrate on the investigation of teachers‟ knowledge at the mathematical
horizon of algebra to help the development of students‟ understanding of algebra in middle
school grades.
This study presents an opportunity to discuss teacher knowledge as topic specifically
within different components. As further research, on a qualitative level, the number of
teachers can be increased, and, on a quantitative level, research can be carried out to make a
generalization for teachers‟ knowledge of algebra by developing CK and PCK tests.
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