Diagnostic thinking of in-service teachers in inclusive mathematics education: A video vignette-based study

Diagnostic thinking is understood as a central component of teachers’ diagnostic competence, encompassing processes of perception and interpretation that shape instructional decision-making. This study investigates primary and special education teachers’ diagnostic thinking when perceiving and interpreting students’ solution processes in real-world problems in inclusive classroom settings. Data were collected through semi-structured interviews using video vignettes of students working on such problems. The findings reveal both shared and distinct patterns in diagnostic thinking. While both groups attend to number range and operational understanding, primary education teachers show a more differentiated diagnostic repertoire. Special education teachers focus more strongly on foundational competences, reflecting their professional emphasis on basic learning prerequisites. These findings may indicate the importance of mathematics-specific pedagogical content knowledge in shaping diagnostic thinking and suggest that professional background influences how teachers perceive and interpret students’ mathematical thinking.