Teachers in mathematics not only need a deep understanding of mathematics but also need knowledge on how to teach the mathematics (Ball & Bass, 2003; Grossman, 1990; Ma & Kessel, 2000). How to teach such Mathematical Knowledge for Teaching (MKT) was the focus for the study described here. Five aspects of MKT were chosen to work with. The goal was to improve student teachers' understanding of the relations between these five aspects, or "interrelating components". The components chosen were: pupils' preconceptions, models for explanation, related (hands on) materials, suitable exercises and curricular knowledge. A Learning Study as a form of design research, was conducted where four critical features concerning MKT were found.