Routes into teacher training have expanded in recent years, accompanied by a growing interest in schools 'growing their own' teachers from amongst support staff. However, little attention has been paid to their transition to the role of teacher. This article investigates influences on identity development and the extent to which personal values are reconciled with professional demands and socially constructed facets of educational practice. Participants were nine staff in one secondary school for pupils with moderate learning difficulties who had undertaken the transition from LSA (learning support assistant) to teacher. Qualitative data were obtained through an online survey and focus group discussion. Findings show that extensive opportunities to experiment with provisional and possible selves, immersion in educational discourse, classroom agency and staff collaboration engender a 'teacher' self-concept and positive motivations for LSA career development, and that self-esteem and self-efficacy are strengthened by how an individual's values align with those of the setting in which they work. Findings may inform school leaders as to the value of training teachers 'in-house' and support career development decisions of LSAs, a pathway of potential significance given the current pressures on teacher recruitment and retention.