This case study of a preservice secondary mathematics teacher focuses on the teacher's beliefs about his role as mathematics teacher. Data were collected over the final 5 months of the teacher?s university teacher education program through interviews, written course assignments, and observations of student-teaching. Findings indicate that the preservice teacher valued classroom roles in which students, rather than the teacher, explained traditional mathematics content. As his student-teaching internship progressed, the teacher began to develop new roles and engaged students in additional mathematical processes. These results emphasize the need for preservice teachers to recognize how teacher and student roles impact interrelationships between understanding and mathematical activity, and illustrate the nature of teacher learning that can occur during an internship.