This case study examines joint reflection in the context of peer group mentoring during the teaching practicum, involving three pre-service teachers and a mentor engaging in discussions supported by the video recorded lessons taught by the pre-service teachers. The approach to joint reflection was non-prescriptive and pre-service teacher-initiated. The roles of the peer group and the mentor are explored in the light of their impact on pre-service teachers' joint reflection process. The findings challenge prior research by demonstrating that pre-service teacher-initiated reflection has the potential to assist peer groups in creating a common language and learning context to acquire practicum knowledge, develop practical tools and build inferential knowledge. The findings also reveal that mentors' role needs not be directive, but they can maintain the role of a co-reflector throughout the peer group mentoring process. The implications for teacher education are discussed.