This study investigates whether the quality of discourse during teacher induction classes predicts beginning teachers' reflection and beliefs about teaching and learning mathematics. In a study with repeated measurements (interval 10 months), transmissive and constructivist beliefs of 536 German teacher candidates in their 2-year induction phase from 100 different seminars were assessed twice by questionnaires. In addition, the teacher candidates' reflection, their motivational-affective resources (self-efficacy, enthusiasm and emotional exhaustion) and their perception of discourse quality in the seminar (discussing different points of view and sharing experiences only) were assessed. Multilevel regression analyses confirmed a mediation effect: In seminars where candidates actively discussed different points of view, they showed higher levels of reflection. Reflection, in turn, was related to increased constructivist and decreased transmissive beliefs. This mediation effect was not found for seminars where experiences were only shared, not juxtaposed. The association between discussing different points of view and reflection was moderated by teacher candidates' enthusiasm and emotional exhaustion. The results support the relevance of deep processing and individual resources for the process of belief change.