As in the case of many other local and overseas teacher-training institutions the Postgraduate Certificate of Education programme (PGCE) at the University of Pretoria is a model rich in experience. In this model 60% of the time is devoted to a school-based programme and 40% to the university-based programme. The school-based programme is presented in association with schools. The student teacher is placed in a school for a period of seven weeks and assigned to a teacher who acts as the mentor teacher. The mentor teacher serves as a the link between teaching theory and subject content and also plays a major role in the contextualisation of the classroom learning experiences. The university prescribes various tasks: mentor teacher have to stimulate the inquiry skills and reflective practices of student teachers, manage meta-communication across situation and role, manage learning tasks and create a safe and challenging learning environment to the students. The mentor teacher should therefore not only be a subject specialist in his or her field of specialisation but should also create the opportunity for student teachers to maximise their potential. In this study the focus is on the experience of the teacher taking up the role of a mentor teacher. To fulfil the role of mentor teacher implies that an exchange of identity needs to take place from teacher identity to mentor teacher identity. This prompted the following research question: What is the identity image of a mentor teacher? With subsidiary questions as <ul> <li>What are the identifying characteristics of a mentor? </li> <li>What are the identifiable dynamic processes or stressful situations that have an impact on the identity formation of a mentor?</li></ul> The research could be identified as qualitative in the interpretative paradigm. Data were collected by means of open-ended questionnaires and in-depth interviews with selected mentor teachers and student teachers. The student teachers assigned to the selected mentors were automatically included in the study. The study was repeated for over a period of three terms, each term with two different teachers and student teachers. To analyse the data, Gee’s (2000-2001) four perspectives of identity, namely nature-identity, institution-identity, discourse-identity and affinity-identity, were used as analytical framework. The results disclosed many indicators supportive of mentor-identity but no fixed mentor-identity emerged. However, the characteristics, functions and responsibilities of a successful mentor in this case study were identified. These characteristics, functions and responsibilities defining the identity of a mentor teacher, could support the school in selecting teachers to take up the role of mentor teachers. In an extended school-based teaching practice the quality of the experience, in most cases, depends on the mentor teachers' beliefs and attitude towards the task.