The specialized literature frequently cites the inclusion of different interest groups in evaluative research, referred to generically as "participatory evaluation". However, there is a lack of an empirical basis for discussion on ways to operate and (especially) qualify such participation. This article discusses the participatory development of mental health indicators for use in the Centers for Psychosocial Care (CAPS) in Brazil. The process included participation by 58 health workers and managers from 26 CAPS through regular meetings over a year. The meetings were intermediated by a course on mental health evaluation and workshops in subgroups, supported by facilitators throughout the year. The creation of spaces for the qualification of their participation, through the course and other collective activities, proved effective for guaranteeing participation at various levels in the process (such as definition of issues, pre-test indicators, and data analysis) as well as for stimulating ownership of the final product by the participants.