In this article, we report on a study of beliefs about mathematics, teaching, and proof conducted with six prospective secondary mathematics teachers as they completed a two-semester sequence of a content course and a methods course. The initial beliefs of the participants were identified using interview and survey data, and potential shifts in beliefs were examined through further interview and survey data combined with classroom observations and written work. While their beliefs about mathematics and proof appeared to be relatively stable, their beliefs about teaching shifted from a more teacher-centered view to beliefs that foreground the activities and understandings of the students. These shifts are analyzed using the construct of belief structures, and activities and events from the courses that may have facilitated the shifts are identified. The results are consistent with the literature in some respects, such as the stability of the participants' beliefs about mathematics. On the other hand, our results present new information about how prospective secondary mathematics teachers' beliefs about teaching may be impacted. (Contains 2 figures and 4 footnotes.)