<p>This paper presents a model for studying the processes involved in mathematics teacher professional development. Specifically, it focuses on professional development programs in which researchers in mathematics education act as teacher educators and collaborate with teachers in designing classroom activities and mathematical tasks for students. The model is constructed by combining the meta-didactical transposition framework, the documentational approach to didactics, and the construct of beliefs. Its evolution is described through an account of the subsequent developments and refinements. A general methodology for data collection and analysis is proposed, aimed at providing a nuanced understanding of the complex processes characterizing teacher professional development. This includes the examination of teachers’ and researchers’ meta-didactical praxeologies, documentation work, and beliefs, as well as the interrelations among these elements. For each version of the model, an example of application is provided to illustrate its modularity and the possibility of partial use. Finally, the application of the complete model in its final version is presented, showing how it can be fruitfully adopted to shed light on different yet complementary aspects of the processes under investigation.</p>