The article focuses on teaching maths in German primary schools out-of-field. The concept of subject matter seems to stand in opposition to the equally pedagogically and administratively desired class teacher principle in primary school. In the contribution, negotiations are outlined on the basis of a qualitative-reconstructive-interview-study, to what extent subject matter exist by primary school teachers who teach mathematics out-of-field. The central question is, can out-of-field primary school teachers train and use biographical and communicative resources for their teaching activities despite the lack of a degree in the subject matter? The study shows that primary school teachers who teaching out-of-field gain biographical and communicative experience, but cannot always call it up as a resource. So that the responsibility does not lie with each individual teacher, but must be established as an institutional and collective anchorage in the system.