Caliskan, EbruAkarsu, MuratNacar, Sema2026-04-042026-04-0420261871-18711878-0423https://doi.org/10.1016/j.tsc.2026.102194https://hdl.handle.net/11616/109390This study investigates the impact of an instructional module, developed within the framework of APOS theory, on enhancing eighth-grade students' conceptual understanding of geometric reflection. The module emphasizes three fundamental components of reflection-line of symmetry, domain, and plane-with the goal of deepening students' comprehension of these concepts and their interrelationships. Changes in students' modes of thinking were analyzed through the lens of APOS theory. Findings revealed that all participating students progressed from the action level to the process level, indicating a shift from viewing reflection merely as a physical movement of shapes to engaging in more sophisticated reasoning based on point correspondences and underlying geometric principles. The module's constructivist, inquiry-based, and discussioncentered activities were found to be effective in promoting this conceptual development. The results suggest that this approach offers valuable implications for mathematics education, particularly in teacher preparation and the cultivation of students' mathematical thinking.eninfo:eu-repo/semantics/closedAccessGeometric reflectionThinking stylesAPOS theoryMotion viewMapping viewArticle6110.1016/j.tsc.2026.1021942-s2.0-105032567633Q1WOS:001718675300001Q1