This study investigates the diagnostic and prognostic framings of Swedish mathematics teachers regarding the difficulties experienced by students in mathematics learning. Collegial discussions among 65 mathematics teachers in nine collegial groups were videotaped during a professional development (PD) program entitled Boost for Mathematics for analysis. The results show that the diagnostic framings of the teachers were mainly attributed to the cognitive abilities of students, whereas the prognostic framings were mainly related to lesson organization such that students should collaborate. While the teachers emphasize collaborate group work, they put little emphasis on how they could act in these learning situations. These results contribute to the understanding of Swedish mathematics teachers' framing of students' difficulties in mathematics learning and to the role of collegial discussions in PD initiatives.