The impact on teachers’ task performance in the classroom appears to be higher when mentor teachers are trained (Evertson&Smithey, 2001; Giebelhaus& Bowman, 2002). As a consequence, many schools, often in cooperation with teacher education institutions, implement training programmes to broaden mentor teachers’ supervisory repertoires in mentoring dialogues (Strong & Baron, 2004). The present study has been carried out in the context of the development and implementation of such a training programme.