This chapter explores one way of formatively assessing student teachers’ development of their learning about teaching science. This chapter is based on the use of formative interactions as a way of understanding how their learning develops. In so doing, this chapter also offers insights into how student teachers’ professional learning might be catalysed and enhanced. The data for this study is based on a primary science teacher education research project (N = 24 participants) that aimed to connect research on [formative] assessment with the development of student teachers’ learning to teach science, and, as a consequence, sets out to illustrate how an articulation of this knowledge might inform approaches to science teacher education. The results of this project highlight the potential to positively focus student teachers’ self-reflection and self-assessment through formative interactions.