The quality of mentoring in teacher education is an essential component of a powerful learning environment for teachers. There is no single approach to mentoring that will work in the same way for every teacher in each context. Nevertheless, most mentor teachers hardly vary their supervisory behaviour in response to varying mentoring situations. Developing versatility in mentor teachers' use of supervisory skills, then, is an important challenge. In this chapter, we discuss the need for mentor teacher preparation and explain the focus, content, and pedagogy underlying a particular training programme for mentor teachers, entitled Supervision Skills for Mentor teachers to Activate Reflection in Teachers (SMART). Also, findings from several studies assessing mentor teachers' supervisory roles and use of supervisory skills in mentoring dialogues, before and after the SMART programme, are presented. In addition, implications and perspectives for mentor teacher development and preparation are discussed.