The paper presents and discusses an ATD based (Chevallard, 2012) model of theory-practice relations in mathematics teacher education. The notions of didactic transposition and praxeology are combined and concretized in order to form a comprehensive model for analysing the theory-practice problematique. It is illustrated how the model can be used both as a descriptive tool to analyse interactions between and interviews with student teachers and teachers and as a normative tool to design and redesign learning environments in teacher education, in this case a lesson study context.