The Montréal Longitudinal Study of Disruptive Boys, an experimental study, was designed to understand boys who were considered disruptive in kindergarten. One part of the study involved assessing effects of a preventive treatment program carried out during the boys' early years in primary school. This paper reports on the outcome of the randomized treatment experiment 3 years after treatments ended. Disruptive boys were randomly allocated to a treated group and two nontreated groups. Treatment consisted of parent training and training of boys for social skills, fantasy play and television viewing. Results suggest that the treatment program had some positive effects. Some of the improvements were not evident immediately after treatment ended.