[eng] This study analyzes adherence to a universal family prevention program used in schools, the Universal Family Competence Program 11-14. It reports on the family members' retention rates, attendance and quality of participation in the sessions, as well as family satisfaction with the trainers and the program itself. The study, based on a quasi-experimental design with pretest and posttest measures and experimental and control groups, evaluated fidelity and the effectiveness of the mechanisms used to control the program conditions. The results point to the need for the inclusion of methodological strategies aimed at facilitating assessments of the multiple dimensions of adherence and at guaranteeing optimal family participation rates.