Inclusive educational leaders promote teacher team functioning. To support leader inclusiveness, we designed and implemented a faculty development programme focusing on leader identity formation. We investigated (1) how participants' leader identity developed throughout the programme and (2) how the design principles contributed to this process, according to participants. A design-based research approach was followed. Participants were 7 course coordinators, leading an interdisciplinary teacher team. To study leader identity development, participants repeatedly filled out a validated questionnaire. To investigate how design principles contributed, observational field notes, facilitator debriefings, a programme evaluation questionnaire and a semi-structured focus group were used. Thematic analysis was applied for qualitative data. Participants gained broader views on leadership, moving from individual dominance towards engaging team members. Most participants initially experienced a deconstruction of their former leader identity and became motivated to improve leadership qualities. Competence-building, reflecting and receiving feedback on workplace experiences, and practicing in a safe environment were perceived to be key for identity development. We developed and evaluated a leader identity programme which can convert teachers' classic leadership views towards views incorporating social interactions and relationships. We demonstrated how social interactions provide opportunities to learn from pe.ers in the work environment.