The concept of Mathematical Knowledge for Teaching (MKT) was introduced by Ball and colleagues (Ball, Thames & Phelps, 2008), building on Shulman’s (1986) notion of Pedagogical Content Knowledge. MKT is ‘the mathematical knowledge needed to carry out the work of teaching mathematics’. In this project, a team of researchers at two Irish universities studied the development of MKT in two groups of pre-service teachers. The project aimed to help students develop their own MKT, and to develop a richer conception of the role of mathematics content knowledge in teaching, through a series of workshops designed and delivered by the authors. The students’ awareness and level of MKT was investigated using pre- and post-intervention questionnaires. We describe the intervention and present the findings from the analysis of the data collected. In particular, we describe how the group’s view of the mathematical work of a teacher changed over the course of the project.