At the current stage of development in the family therapy field, exploratory, small-scale process studies are necessary in order to understand through what interpersonal processes child and family change occur. The goal of this article is to show how relevant therapist-parent interactions within family-based approaches can be explored and linked to the reduction in childrearing and behavior problems. Sequential analyses on 13 treatments using the Family Project Approach revealed that, within the most successful treatments, therapist and parent interact in a collaborative way in the phase of Direct Influence. In the beginning of this treatment phase, the therapist must activate the parents to tackle the problems actively. Further explorations indicated that a collaborative interaction pattern between therapist and mother during the first three sessions of therapy contributes to a better outcome.