This paper focuses on the complexity and difficulties of identifying and developing student teacher's Pedagogical Content Knowledge during pre-service education. An empirical study was conducted on six primary science student teachers' learning in school practice when teaching pupils aged 9-11 in physics during a year. One third of the lessons were videotaped and the student teachers were later interviewed using the video tape for stimulated recall. Participants reflected on the pupils' and their own language and actions in the classroom and discussed their professional teaching ability and their own conceptual understanding of physics. The study emphasises the role of teaching experience and reflection in science teacher education and discusses strategies associated with integrating the practical and the theoretical in teacher education to create opportunities for student teachers to develop their PCK.