Investigation of the change of a middle school mathematics teacher's mathematical discourse on quadrilaterals

In this research, it is aimed to investigate the change of mathematical discourse of a middle school mathematics teacher on about 5th grade quadrilaterals subject with the commognitive approach in the context of lesson study model. In the research, case study has been adopted from qualitative research patterns. The participants of the research, which was conducted in a public school in the province of Düzce, are two middle school mathematics teachers working at the same school. Criterion sampling, one of the purposive sampling types, was used to identify the participants. The data of the research was collected over a two-month process in the second semester of 2017-2018 academic year. In the process of data collection, classroom observations, audio recordings of lesson study meetings and documents were used. In the research process, three lesson study cycles as two pilots and one original were conducted. In the period of each lesson study, two teachers performed the practice but only one teacher's practice was included in the analysis. The teacher's discourses prior to the lesson study and in the process of applying the lesson study were analyzed and compared according to the Commognitive Approach. As a result of the research, it was concluded that the studies carried out during the lesson study process deepened the knowledge of teachers about the teaching of quadrilaterals and quadrilaterals and also improved teacher discourse during the teaching of quadrilaterals.