A crucial competence for mentor teachers is the ability to analyse classroom practices as they are expected to model effective teaching practices and to provide feedback to student teachers. This ability is referred to in the literature as professional vision. The present study assesses mentor teachers' (n = 137) professional vision regarding teacher-student interactions and differentiated instruction, using a validated video-based comparative judgement measurement instrument. The results indicate that mentor teachers have a high professional vision. It can thus be assumed that mentor teachers can support student teachers. Additionally, their professional vision is compared with that of classroom teachers (n = 996) and student teachers (n = 2168), expecting it to be significantly higher than that of classroom teachers and student teachers. The results show no significant difference between mentor teachers and classroom teachers but a significant difference between mentor teachers and student teachers. Hence, mentor teachers and classroom teachers are equally able to identify and interpret crucial aspects of effective teaching behaviour and both groups are better able than student teachers in this regard. This study contributes to the current state of the art on mentor teachers from a theoretical, empirical and methodological point of view.