In some places it will require very good training to establish it successfully. There is no automatic reason why even a good practitioner should be good at articulating what underlies their practice, so it is very important to give them the tools to do the job. Brighton is considering giving mentors one module's credit in its MA programme. Some courses make attendance compulsory, but not satisfactory completion. If the University has validated the course, it should be satisfied with what it learns at the end.
Formative judgements are only for the course itself.
TVU has a process of peer appraisal for staff development - participants provide their own information into this. But Departments do have a quality assurance role. Bewrae the danger of a course favouring those who are good at the process of reflection but perhaps not at teaching. A few staff positively refuse to take on this process. To viva every body would be a heavy workload.