The present study investigated how student teachers and mentor teachers in a one-school-year teacher practicum in Germany interacted in an 'egalitarian' way despite their experience-based gap in expertise, status and power. Our study is embedded in a participatory research context to involve the agents of change. The sample consisted of 57 student teachers and 98 mentor teachers in primary and lower secondary education. We used the critical incidents technique; critical incidents were collected through focus group discussions and analysed by qualitative content analysis. Egalitarian interaction was achieved through the participants flexibly changing roles in providing and receiving feedback and the use of an 'experimental room' where both student teachers and mentor teachers could reflect on and develop their teaching practice (through co-constructive knowledge creation while working together on teaching-related activities). For student teachers, being assigned the status of a 'colleague' demonstrated egalitarian interaction. Implications for developing participatory-involved mentoring concepts were discussed.