How do high school mathematics teachers engage in reflective practice when developing didactical design?

Reflective practice serves as a critical strategy for safeguarding the professional identities of mathematics teachers, ensuring that the development of didactical designs transcends mere administrative compliance. Drawing upon the Theory of Didactic Transposition as a theoretical lens, this qualitative study aims to how 15 Indonesian high school mathematics teachers integrate reflective practice into didactical design formulation. Using Interpretative Phenomenological Analysis (IPA), data were gathered via semi-structured interviews and documentary analysis. The findings reveal two distinct realities: (1) didactical design without reflective practice, characterized by external resource dependency and compliance-driven administrative formality; and (2) design integrated with reflective practice, prioritized based on the mathematical abilities of learning cohorts, curriculum adaptation, the alignment of instructional models with mathematical concepts, student assessment results, and individual learning processes. Overall, results indicate that teachers inconsistently align the four nodes of didactic transposition—mathematicians, curriculum, teachers, and students. Consequently, the study proposes a framework serving as a navigational compass to help teachers build resilient professional identities amidst policy and administrative pressures.