The school-based experiences of preservice teachers are much reported in research with school placement often presented as a `high stakes' endeavour. However, there is limited research on the impact of their presence on supervising teachers. This paper highlights supervision as bringing a change to teaching that impacts on teachers' identities. Tensions can emerge when teachers are required to act concurrently as teacher and supervisor. The paper argues that it is critical that the interpersonal demands of supervision become an important focus of the partnership between universities and schools if practicums are to be beneficial to all stakeholders.