The overall aim of the present research project is to empirically investigate what inclusion in mathematics education can be and how it is possible to develop inclusive mathematics education, based on special educational needs in mathematics. In this paper, the aim is to present how the impact of the principal affects the development of inclusion in mathematics from a teacher perspective. The study has an ethnographic approach, where a large primary School is being studied.  The results indicate that the principal’s impact on inclusion in mathematics at the realisation arena is relatively weak. In this study, inclusion in mathematics has strong connections with didactical issues.