The objective of this study was to develop a school-based substance treatment model and evaluate the feasibility and preliminary outcomes of treatment in a school-based setting to improve access to treatment for adolescents with substance use disorders. This study provided care to 41 youths (12 to 18 years old) in three school-based health clinics. The intervention consisted of 12 weeks of individual motivational interviewing, acceptance and commitment therapy, contingency management with urine drug screens, medication-assisted therapy, family sessions, and case management. Feasibility outcomes included the number of sessions attended, the Session Rating Scale, and qualitative feedback from patients (N = 41), therapists (N = 3), and a school principal. Preliminary treatment outcomes included the Timeline Followback Interview, a modified Outcome Rating Scale, and a questionnaire of school engagement. The average number of sessions completed was 7.4 (SD = 3.6), and the average Session Rating Scale score was 38.2 (0 = minimum alliance, 40 = maximum alliance). Qualitative interviews provided feedback to adapt the treatment model further. Youths reported significant pre-post improvements in emotional wellness, school engagement, and substance use. This study produced a school-based substance treatment model that is well-received by patients, demonstrated feasibility, showed positive preliminary outcomes, and is ready for further clinical testing.