The objective of this paper is to describe the means by which the principal affects the process of inclusion in mathematics from a teacher perspective. Two notions form the theoretical foundation: participation and inclusion. The participatory perspective is provided by Wenger’s theory of communities of practice (1998). When discussing inclusion, Asp-Onsjö’s (2006) notions of didactical, spatial, and social inclusion have been used. The results are presented in two parts: the first presents identified communities at the investigated school and the second identifies codes of impact pointing towards inclusion in mathematics. When combining the participatory and the inclusive perspectives, codes of impact regarding inclusion in mathematics in the different communities were identified. Although there are different codes of impact in the different communities, one can identify several recurring codes when investigating the impact of the principal. The most frequent is courses. Competence, didactical discussions and planning also recur in the different communities. Investigating these codes of impact, there appears to be a gap between the steering of the principal and what actually occurs. The results indicate that the principal’s impact on inclusion in mathematics in the realisation arena is relatively weak.