We attempted to examine the effects of adolescent groups on collective problem behaviors. Based on our group process model, we predicted that the more frequently did adolescents engage in collective problem behaviors, the lower was the self-control in their groups (Hypothesis 1), the lower was the adolescents' self-control (Hypothesis 2), and the more strongly they committed to the low-self control groups (Hypothesis 3). We made 130 male students in professional schools describe the groups to which they belonged when they were in high school, and rate their own level of self-control, that of the groups, their level of commitment toward the group, and the frequencies of collective problem behaviors. The results supported Hypotheses 1 and 2. Although Hypothesis 3 was not supported, it was found that the adolescents who strongly committed to groups engaged in collective problem behaviors more frequently.
