This paper presents a theoretical model for the development of knowledge for teaching, based on a study of primary pre-service teachers (PSTs) in their final year of an Initial Teacher Education Programme. This model arose from findings about PSTs' perceptions of knowledge for mathematics teaching that were related to knowledge of the curriculum, mathematical content knowledge and knowledge of school contexts. The theoretical model describes how PSTs developed this knowledge for teaching mathematics. There are three phases in this model; "recognising" crucial aspects of teaching, "reconceptualising" these aspects, and "realizing" these aspects in a mathematics classroom. In conclusion I discuss the possible use of this model for my work as a teacher educator.