The present study uses Dialogical Self Theory to explore the extent to which a dialogue supports teachers' professional identity development. Using a narrative approach that includes interviews, observations of educational activities and collective meetings, insight is gained into teachers’ I-positions, meta-positions and promoter positions. The findings suggest that a dialogue, in which teachers talk about boundary experiences and articulate I-positions, stimulates teachers to reflect on their teaching behaviour from a meta-position and enables them to harmonise their multiple I-positions. Moreover, it stimulates teachers to develop their identity as a teacher and to change their teaching behaviour. Display omitted •A dialogue stimulates teachers' professional identity development.•Boundary experiences are needed to start a dialogue.•A dialogue encourages teachers to change teaching behaviour.•Strong self-perceptions (I-positions) hinder teachers' professional identity development.