Monitoring the development of 7th grade students' geometric thinking levels using the Van Hiele instructional framework in quadrilateral instruction

The aim of this study is to examine the developmental process of 7th grade students' geometric thinking levels on the topic of quadrilaterals through instruction based on the Van Hiele instructional framework.Conducted within the scope of a teaching experiment design and using a qualitative research approach, the study was carried out with four students of varying academic achievement levels from a public middle school in Yozgat, Turkey. The researcher also acted as the students' mathematics teacher during the instructional process. Data were collected through focus group interviews conducted throughout the process and written documents from students' worksheets. The instructional process was planned based on the five learning phases of the Van Hiele model, and five- phase lessons were implemented for each type of quadrilateral. The implementation was conducted over 13 sessions, and the data were analyzed using descriptive analysis. The findings obtained through MAXQDA software were visualized using conceptual maps. The results indicated that students were predominantly at Level 1 at the beginning; however, a noticeable transition to Level 2 occurred during the process, and instances of Level 3 thinking were observed in the final sessions. No examples of thinking at Levels 4 or 5 were observed. More significant developments were noted in thinking related to shapes such as squares, parallelograms, and rectangles; students began to express the hierarchical relationships among these shapes more clearly. Structured activities and the phased instructional approach supported upward development in thinking levels. In this context, the study demonstrates that the Van Hiele instructional model provides an effective teaching approach for understanding the concept of quadrilaterals and fostering geometric thinking. The student-centered and structured teaching process, particularly by encouraging thinking at the analysis and deduction levels, facilitated deeper learning compared to traditional approaches. 2025, xii + 109 Pages Keywords:Van Hiele instructional model, Geometric thinking levels, Quadrilaterals, teaching experiment, Middle school mathematics education.