The authors have been conducting research with early career secondary mathematics teachers in metropolitan Sydney, focusing particularly on the professional experiences of student teachers. As part of the research, twelve supervising teachers were visited at their schools. Seven of them were interviewed individually about their role in developing the knowledge and skills of student teachers during the professional experience. The remaining five teachers were unavailable for interview and responded to the core interview questions in a written survey. The teachers had a range of experience in the classroom (4-30 years) and in supervision (1-20 student teachers). They were asked why they had decided to take on their mentoring role and about the benefits they and their students gained from having a student teacher in the classroom. Here, their responses are summarised.