This research aimed to understand what physics and chemistry pre-service teachers learn within pedagogical content knowledge in a lesson study with the topic speed of sound, 8th grade. Participants were three pre-service teachers. This was a qualitative and interpretative study. Data were collected from participant observation, individual interviews and individual written reflections. Results showed that the participants developed their pedagogical content knowledge, when they identified the students' prior knowledge and when they discussed strategies to help students overcome their difficulties. [For the full proceedings, see ED619611.]