The aim of this paper is to develop science teachers ́ PCK through their participation in a learning study. The research question that frames the study is “How do science teachers ́ learning about science teaching (PCK) develops as a shared practice through their participation in a learning study? As such, the project aims to investigate how teachers ́ increased (or not) professional knowledge of teaching is enhanced, and further, how students ́ learning might be developed as a consequence. During one semester, three secondary science teachers and a science education researcher worked together in a learning study in which the object of learning was to understand the concept of ion and how ions are formed. Data were collected from video recorded lessons and stimulated recall sessions in which the teachers and the researcher reflected on the lessons to analyze how the teachers developed knowledge of students learning and the impact of that knowledge on their own teaching. The results indicate that teachers ́ participation in the learning study proved to be helpful in their (re)considerations of their science teaching in that it points to the particular role of research-based learning in providing a metacognitive lens through which to analyze science teaching and learning.