The aim of this paper is to show how external influences need be considered when discussing the formation of a primary school mathematics teacher. The external participation will be illustrated by the case of Evie, a student teacher. Two conceptual frameworks have been used, System Functional Linguistics and Patterns of Participation. The first has been used as a methodological tool and the second as an analytical tool. The results show that Evie’s external prior and present participation might have an impact on her process of becoming a primary school mathematics teacher inside teacher education.