Objectives: The purpose of this study is to test whether increasing the exposure to coaching by adding an in-home component to clinic-delivered Parent-Child Interaction Therapy (PCIT) will increase the speed of parenting skill acquisition and show greater improvements in children's behaviors and parental stress. Methods: Seventy-three parent-child dyads participating in clinic-based PCIT are randomly assigned to an adjunct PCIT or Social Support treatment group. The sample of children is 58% male and ranges in age from 1.7 to 8.2 years. Results: Analyses show that participation in adjunct PCIT services is associated with greater use of positive verbalizations and leads to improvement on measures of parent functioning. Conclusions: The meaning of these findings with respect to change and the process of treatment is discussed. (Contains 5 tables.)