START NOW: a cognitive behavioral skills training for adolescent girls with conduct or oppositional defiant disorder – a randomized clinical trial

Background Conduct disorder (CD) and oppositional defiant disorder (ODD) both convey a high risk for maladjustment later in life and are understudied in girls. Here, we aimed at confirming the efficacy of START NOW, a cognitive‐behavioral, dialectical behavior therapy‐oriented skills training program aiming to enhance emotion regulation skills, interpersonal and psychosocial adjustment, adapted for female adolescents with CD or ODD. Methods A total of 127 girls were included in this prospective, cluster randomized, multi‐center, parallel group, quasi‐randomized, controlled phase III trial, which tested the efficacy of START NOW (n = 72) compared with standard care (treatment as usual, TAU, n = 55). All female adolescents had a clinical diagnosis of CD or ODD, were 15.6 (±1.5) years on average (range: 12–20 years), and were institutionalized in youth welfare institutions. The two primary endpoints were the change in number of CD/ODD symptoms between (1) baseline (T1) and post‐treatment (T3), and (2) between T1 and 12‐week follow‐up (T4). Results Both treatment groups showed reduced CD/ODD symptoms at T3 compared with T1 (95% CI: START NOW = −4.87, −2.49; TAU = −4.94, −2.30). There was no significant mean difference in CD/ODD symptom reduction from T1 to T3 between START NOW and TAU (−0.056; 95% CI = −1.860, 1.749; Hedge's g = −0.011). However, the START NOW group showed greater mean symptom reduction from T1 to T4 (−2.326; 95% CI = −4.274, −0.378; Hedge's g = −0.563). Additionally, secondary endpoint results revealed a reduction in staff reported aggression and parent‐reported irritability at post assessment. Conclusions Although START NOW did not result in greater symptom reduction from baseline to post‐treatment compared with TAU, the START NOW group showed greater symptom reduction from baseline to follow‐up with a medium effect size, which indicates a clinically meaningful delayed treatment effect.