Mathematics Teachers' Use of Mathematical Descriptions, Explanations and Justifications: The Case of Samet

It is important for teachers to design and use mathematically accurate descriptions, explanations and justifications that are comprehensible and useful for students in the context of reflecting their mathematical knowledge for teaching. The purpose of this study is to examine a mathematics teacher’s mathematical knowledge for teaching function concept by investigating his use of mathematical descriptions, explanations and justifications. The study was conducted as a descriptive case study. The participant in the study was one mathematics teacher (Samet) who volunteered to join the research. Data was collected via observing and recording the teacher’s teaching of the function concept and survey of function concept. The results of the study revealed that the teacher mostly used mathematical descriptions in his teaching. This was followed by mathematical explanations, and mathematical justifications. The teacher’s use of mathematical descriptions, explanations and justifications and his sufficiency at using these varied according to cases. Results indicated some deficiencies in the teacher’s mathematical knowledge for teaching