This study investigated the collaboration of five science teacher leaders in a vertical group, supported by a grant-funded teacher leadership professional development program. It utilized video artifacts of teaching and transcriptions of collaborative meetings to answer the following research question: What happens when science teachers in a teacher leadership professional development program collaboratively examine their teaching in a vertical community of practice? Three themes emerged from the data: (a) Participating in a pseudo community, (b) Emergent versus actual problem of practice discussions, and (c) exploration of practice through reflection, deepening pedagogical content knowledge, and facilitating vertical articulation. Collectively, these themes demonstrate the essence of being an effective teacher leader and importance of a critical friend to engage in authentic discussions around practice and be self-reflective toward instructional improvement.