This study addresses how rehearsals of teaching could support teachers in developing mathematical knowledge for teaching (MKT). The analysis of 30 rehearsals, from elementary methods courses in 3 teacher education programs, attends to what novice teachers and teacher educators did in rehearsal that enlisted MKT. The findings elaborate the tasks that enlisted MKT in practice and the work of the teacher educator in supporting novice teachers' learning of MKT inside the interactive work of teaching.