Children who display more than normal symptoms of defiance and aggression early in life are prone to develop serious externalising behaviour (e.g. conduct disorder and substance abuse). Structured parent-training programs are the most effective treatment for young children with externalising behaviour problems. "The Incredible Years" is a manual-based, parent-training program developed by Carolyn Webster-Stratton. International studies have shown it to be effective.

The project uses "The Incredible Years, a parent development program" with parents of 48 three-to-nine-year-old children with serious externalising behaviour problems. The aim is to test the program in a culture (Sweden) which is rather different from that in which it was developed (USA), and to measure its effects on externalising behaviour problems among pre-schoolers as well as school-aged children. Parents are randomised for immediate treatment or to be put on a waiting-list. Parents of six children meet with two group leaders for a total of twelve sessions during one semester. All in all we treat eight groups (four pre-schoolers and four school- aged children). Parents on the waiting-list are offered treatment after six months. To better understand which families need additional or alternative help we measure different child and family factors thought to be predictive of treatment outcome, in addition to measures of the children's symptoms. Data is collected at three points in time (before and after treatment and twelve months after treatment completion).