In this study, a learning study was used to enhance prospective teachers' learning about how to teach a specific topic in mathematics or natural science to 4th-6th graders. It has been argued that participating in learning study can direct prospective teachers (PTs) towards the object of learning, and what needs to be enacted in teaching to make it possible for the learners to learn what is intended. However, less is known about what capabilities PTs develop from planning lessons in collaboration with peers and a teacher educator in learning studies. Our research question concerns what opportunities PTs have to develop pedagogical content knowledge (PCK) when participating in learning studies. We analyzed three groups' lesson planning on two occasions, once when planning without a teacher educator, and once when planning with a teacher educator in a learning study using theory-informed questions. The software NVivo was used as a tool to code their discussions concerning PCK. For the three groups studied, there were significant differences regarding possibilities for developing PCK under the two conditions.