The focus of this study is on foundation phase and early childhood teachers’ professional identity formation. This study is about six beginning teachers in their first year of teaching early mathematics, science and technology (MST) in different schools and grade levels. Early childhood settings and primary schools in South Africa have a diverse learner body that increasingly demands of beginning early childhood and foundation phase teachers to continually strive to adapt their teaching and young children’s learning to the different learning environments for effective implementation of the curriculum. A learning identity framework was used to generate and analyse data. The learning identity framework is premised on the assumption that identity and learning are closely linked and that both are influenced by factors internal and external to the individual. Specifically, the study sought to answer the research question of how beginning first year early childhood and foundation phase teachers form, sustain or change their professional teacher identity in the teaching of mathematics, science and technology (MST) in the early years and in different school settings. The study used a phenomenological approach and case study method to explain the professional teacher identity formation process and to illuminate what factors influence this process. The study researched how teacher identities can be narratively constructed on the basis of the lived experiences of the six teachers in different school contexts. Data was generated from different sources for the purpose of triangulation which included visual and written narratives, observations and interviews (open and semi-structured). The analysis and results were based on categories of descriptions of themes. The findings indicate that identity formation is an ongoing process of integration of teachers’ personal and professional histories and initial teacher education and training, alongside issues of school culture and institutional (in-school) support. Those key factors emerge as strong determinants of the kinds and the relative stability or otherwise of professional identities which the six teachers develop in the first year of MST teaching, and thus the kind of reform minded teachers they become.