Prochaska and DiClemente's stages of change model facilitate understanding of engagement difficulties in psychosocial intervention processes. We assessed the link between stages of family change and intervention dropout in a sample of 141 families with relational conflicts between parents and adolescent children. Each family member's stage of change was defined according to three criteria: seeing the conflict as a relational problem, assuming part of the responsibility for the dysfunctional relationship, and understanding one's own mental and emotional states and those of the other family members involved in the conflict (mentalization). Our dropout rate for the sample was 41.8% and was higher for immigrant families. We found a strong association between engagement and the contemplation stage of change, particularly the mother's. In family conflict interventions, participation of all the family members is essential so as raise awareness of the relational aspects of the conflict and the shared responsibility for the conflict and its resolution.