Background Patient‐reported outcome measures (PROMs) are recommended by healthcare systems internationally, but there are a number of barriers to implementation. The aim of this research was to examine the impact of training supervisors in using PROMs on clinical practice, given the importance of leadership when changing behaviour. Method Data included pre–post questionnaires from 42 supervisors, interviews after training with six supervisees and nonparticipant observations of nine video‐recorded supervision sessions. Results After training, supervisors had more positive attitudes to administering PROMs and using feedback from PROMs and had higher levels of self‐efficacy about using PROMs in supervision. Conclusions Findings are in line with the growing body of evidence that training child mental health staff to use PROMs may be associated with changes in attitudes, self‐efficacy and use of PROMs.