Incredible Years parent training: What changes, for whom, how, for how long?

• IY parent training evaluation by a RCT with preschoolers with disruptive behavior
• Children in the IY group experienced decreased behavior problems and increased social skills.
• Caregivers in the IY group improved parenting practices and self-confidence.
• Child's age moderation effect suggests that IY prevents decrease in social skills,
• Chain of change: parental self-efficacy – parental practices – child behavior.

The aims of this study were to examine the efficacy of the Incredible Years program (IY) with Portuguese families of preschoolers, moderator and mediator effects, and sustainability of results. Design: randomized controlled design with pre- and post-intervention, and 12 and 18 months assessments. Participants: 124 children aged 3–6 years, at risk of disruptive behavior problems. Children in the IY group showed significant reduction in behavior problems and increase in social skills; caregivers improved parenting practices and self-confidence. Positive clinical and functional impacts were demonstrated. IY was efficacious with a wide range of families. The moderating effect of the child's age suggests that IY prevents a decrease in social skills for the ages covered by this study. Changes in parental self-efficacy affected changes in parental practices, promoting changes in children's behavior. Positive effects were maintained over time.