The increasingly growing heterogeneity amongst children in school classes presents many teachers with major problems. This thesis aims to highlight the beliefs of teachers in regards to heterogeneity. A second central aspect is the examination of how congruent the beliefs of teachers are in relation to their actual actions. Related to this, this thesis also researches into the implementation of constructive methods used by teachers in order to use heterogeneity positively.For this purpose, a selection of primary school teachers from the IMST Project Pool were interviewed by myself and the transcripts then analysed. In the first part of this paper the theoretical foundations are set out and definitions for terms such as heterogeneity, diversity and beliefs are given. The process for choosing teachers and the conduction of the interviews are additionally explained. Furthermore, the necessary hypotheses for answering the research questions are established.In the second half of this paper there is an evaluation using deductively created categories. These serve to verify or falsify the hypotheses and as such to also answer the research questions.