The purpose of this study is to describe the strategies used by a highly regarded, secondary biology mentor teacher to foster a preservice biology teacher’s pedagogical content knowledge (PCK). In this study, the mentoring was exclusively focused on beliefs about effective science teaching and how students’ learn science. The mentor teacher helped preservice teacher understand why he should teach in particular ways. The mentor also helped the mentee develop his topic-specific knowledge of students’ understanding of science by discussing common misconceptions revealed in students’ conversations and examination responses. She modeled ways for the mentee to access students’ misconceptions.