This study is concerned with prospective elementary teachers' beliefs about collaborative problem solving and dialogue in mathematics classrooms. Participants (n = 16) attended an undergraduate module titled "Problem Solving in Primary Mathematics", which was specifically designed to provide them with opportunities in collaborative problem solving and dialogic activities. Students were invited to answer an open-ended questionnaire at the beginning and end of the course. In addition, at the end of the semester, students wrote individual reflective reports commenting on their experiences. Qualitative analyses revealed three areas of beliefs for which positive changes were observed: (a) dialogue and its relation to school mathematics, (b) the characteristics of a "good" interlocutor, and (c) the importance of collaborative problem solving. This paper closes with a discussion concerning the implementations of our findings and suggestions for future research.