This study focuses on a group of preschool student teachers´ reflections of their Pedagogical Content Knowledge (PCK) during a 10-week music methods course. The student teachers created Content Representations (CoRe) when planning before and reflecting after their music lessons in a preschool context. The analysis of written reflections in CoRe protocols about the teaching of “Dynamics” indicates changes in focus between CoRe 1 and CoRe 2, suggesting a development of PCK. More specifically it was a progress from children gaining experience to children´s understanding, from teaching strategies to children´s learning, and from the teacher governing the activity to involve children collaboration. In conclusion, this approach to enhancing preschool teachers´ professional development in music adapting a CoRe based methodology has a promising potential to make their PCK more explicit and elaborate.