This article focuses on the professional identity formation of six beginner teachers (three in early childhood education and three in the foundation phase), involved in the teaching of Mathematics, Science and Technology (MST). Attention is in particular being paid to the role of professional identity in how they applied innovative teaching methods such as enquiry-based teaching. The study is based on the personal narratives of the six teachers, regarding their own learning experiences in MST, the impact of their professional training at an institution of higher education, as well as their first experiences as MST teachers in the workplace. A qualitative research design was applied and data was obtained through visual (photo collages) and written stories, observation and interviews. Whilst all the teachers held negative attitudes towards Mathematics, this situation was turned around during their university training. The three teachers in early childhood education experienced their entrance to the profession as positive, due mainly to the support of colleagues in their application of innovative teaching methods. Two teachers in the foundation phase, however, experienced the opposite. The findings emphasise the complex processes in the moulding of a professional teacher identity and how teaching practices are influenced by these processes.