Mentor teachers need a versatile supervisory skills repertoire. Besides taking the prevalent role of daily advisor and instructor, mentor teachers should also be able to stimulate reflection in student teachers. Video recordings were analyzed of 60 mentoring dialogues, both before and after a mentor teacher training aiming at developing the encourager role. Mentor teachers' repertoires of supervisory skills were found to consist of an average of seven supervisory skills. After training, a shift was observed in the frequencies and duration with which supervisory skills were used. Although considerable inter-individual variability existed between mentor teachers, training positively affected the use of supervisory skills for stimulating reflection in student teachers.