Building specialized knowledge in geometry: a teaching experiment in initial teacher training

This work aims to characterize the specialized knowledge built in a primary teachers initial training class by means of a task based on video analysis. We designed a first phase consisting in a small scale teaching experiment with three students, used to define the referents that would allow to redesign the task in the second phase. This second phase scaled up the experiment to group of students in a teacher training program. The task was based on the visualization and discussion of a video about building a definition of 'polygon'. After the analysis, conducted using the Mathematics Teacher's Specialized Knowledge model, we identified the knowledge mobilized by prospective teachers about the definition of 'polygon' and its elements, about the mathematical practice of defining, about resources and examples to define 'polygon', about learning difficulties related to that content, and about its presence in primary school syllabi, consistent with research literature. This work ends with reflections about how the task allows to build elements of specialized knowledge.