Abstract Background Peer-assisted learning (PAL) – where students take up a teaching role at an early stage of their training—is widely used in medical curricula. Many qualitative studies have investigated the perceptions and benefits of PAL, but no studies have longitudinally explored how peer teachers experienced their development. This could allow for a better understanding of PAL. In this study, we explored the perceived impact of being a peer teacher on the development of personal and professional competencies as a medical student. Methods We longitudinally conducted semi-structured interviews with peer teachers, during their 2-year teaching period in the skills lab at the University of Antwerp and applied descriptive thematic analysis. Results In total we gathered 47 interviews in 13 peer teachers (9 female, 4 male,. 1–7 interviews each). Peer teachers reported an increase in self-confidence, which gradually transformed into self-efficacy in clinical and teaching skills., Participants told us to be inspired by the previous generation of peer teachers. Their motivation shifted from personal benefits to benefiting others while becoming a role model themselves. The peer teachers illustrated how they developed maturity by integrating different CanMEDS roles. They grew in reflection, changed/transformed an initial mark-driven study drive into more patient-centered ambitions, and started developing a personal style. Conclusions Our study suggests that being a peer teacher leads to more self-efficacy, in clinical and teaching skills, to become a role model with as motivation to benefit others and to grow towards a good doctor maturity. Although the task is to teach peers, this opportunity nurtures the practice and integration of various CanMEDS roles, not only that of scholar but also communicator, collaborator and leader, thereby positively influencing their personal and professional development and their identity as a doctor (professional role).