Substance use disorders among youth remain a serious public health problem. Although research has overwhelmingly supported the use of evidenced-based interventions, one of the primary limitations of the current evidence base is that for the vast majority of treatments, the developers of the treatments are also the ones conducting research on them, raising the possibility of allegiance bias. The present study was an independently conducted randomized controlled trial (n = 126) comparing an evidenced-based treatment for adolescent substance use, Adolescent-Community Reinforcement Approach (A-CRA), and assertive continuing care (ACC), to services as usual (SAU) provided by a juvenile probation department. Latent growth curve modeling was used to compare the treatments on change in substance use assessed by the Global Appraisal of Individual Needs (GAIN) at baseline and 3, 6, and 12 months following treatment entry. All youth evidenced a substantial reduction in substance use frequency and substance-related problems following treatment; however, youth treated with A-CRA/ACC evidenced a substantially greater decrease in substance-related problems. Results are consistent with studies conducted by A-CRA/ACC model developers supporting the effectiveness of the clinical approach and, because the outcomes resulted from an independent replication, are encouraging for the transportation potential of A-CRA/ACC.