During their practical training, feedback for preservice teachers should address the demands of diverse classrooms. Using the critical incident technique within a participatory research framework, this study investigated whether and how mentors adjust their feedback in this regard. Based on a sample of 33 preservice teachers and 46 mentor teachers in German primary and lower secondary education, the results indicate that although pupils’ differing prerequisites clearly presented challenges for preservice teachers, only part of the mentors referred in their feedback to these demands. Mentors who adapted their feedback referred to well-known methods for addressing differences in pupil performance and background and suggested specific novel strategies by specifying what is possible and expedient (or not) when pupils’ prerequisites and backgrounds differ. These methods were found to enhance preservice teachers’ self-efficacy and competencies in teaching diverse classes, and mutual diversity-oriented feedback also benefited mentors. In conclusion, the study identifies implications for feedback development.