Özet:

The aim of this study is to determine the geometric thinking levels of the 8th grade students and to examine the geometric thinking levels of these students in-depth by revealing the differences discoursively. The research was carried out with the 8th grade students in a public school in Gaziantep. Geometric thinking levels of a group of the 8th grade students consisting of 54 students were determined, and then interviews were conducted with six students who were at the first, second and third geometric thinking levels. The study was defined as a case study. In the study, the data were collected in two sections. In the first section, the "Global Van Hiele Questionnaire,” which was adapted to Turkish by the researcher was applied. In the second section, interviews were held with the six selected students. In order to reveal the mathematical discourses of the 8th grade students, the answers given by the students were analyzed by content analysis method. In this study, Sfard's (2008) "Commognitive" theory was used to examine students' mathematical discourses. The discourses of the students were classified and examined in four properties (word use, visual mediators, routines, and endorsed narratives). The results of the study showed that the geometric thinking levels of the 8th grade students were lower than expected (third geometric thinking level). It was also found that even if the students were at the same geometric thinking levels, they did not make the same level of progress with certain geometric shapes. Therefore, it is recommended that teachers pay attention to the discourses of the students.