Cognitive-behavioral therapy (CBT) is used to treat children and adolescents with depression. Researchers determined that many individuals undergoing CBT and other therapies experienced sudden gains, meaning that they experienced a rapid and large improvement in their symptoms between sessions. The studies demonstrated that by the end of treatment, individuals who experienced sudden gains were significantly less depressed and had better long-term outcomes than individuals who did not experience sudden gains. Previous studies investigated sudden gains in individual therapy while the present study examined sudden gains in group treatment. In addition to replicating results of previous studies, the present study sought to examine the effect of sudden gains on depressive symptoms, family environment, cognitive triad, and negative life events at pre-treatment and at a one year follow-up using multivariate analysis of variance. Participants included 136 girls, aged 9 to 13, in two treatment conditions (CBT, CBT+ parent training (CBT+PT), and a Minimal Contact Control (MCC)). At pre-treatment, post-treatment, and at a one year follow-up, participants completed self-report measures of the family environment, cognitive triad, and negative life events. They also completed a semi-structured diagnostic interview designed to symptoms of depression. After beginning the study, participants’ depressive symptoms were monitored with a brief symptom interview and/or a self-report measure of depressive symptoms. Findings from the study provided further evidence that sudden gains occur during group CBT, and that the majority of sudden gains occur early in CBT. The number of sudden gains did not vary significantly by treatment condition, and similar to previous research, the presence of a parent intervention component did not appear to significantly change the relation between sudden gains and treatment outcome. One important finding was participants in the Minimal Contact Control group experienced sudden gains despite not being in treatment. Another important finding was that the participants who experienced sudden gains differed significantly from the participants who did not experience sudden gains on pre-treatment measures of family environment and the cognitive triad but no differences were found at post-treatment or at a one year follow-up. Implications of these results, limitations, and recommendations for future research are provided. / text