This article presents initial results of a research project which investigates subjective theories and typical action strategies of teachers and student teachers in dealing with heterogeneity in school with a focus on the subject mathematics. These results are ultimately intended to contribute to the development of future teaching approaches. To reconstruct subjective theories of teachers and student teachers, group discussions were carried out. The initial results show the aspects of heterogeneity the participants deem important and the possible actions they discern for coping with pupil diversity.