Mathematical knowledge is critical for teachers before they can help students to learn. Ball (1988b) remarked that "knowledge of mathematics is obviously fundamental to being able to help someone else learn it" (p. 12). The importance of teachers' mathematical knowledge for the improvement of mathematics teaching and learning was further advocated by Ball, Lubienski, and Mewborn (2001). Content knowledge does influence the decisions teachers made about classroom instruction. When a teacher has a conceptual understanding of mathematics, it influences classroom instruction in a positive way (Fennema & Franke, 1992). Thus, it is essential that teachers need to competent in their