PROJECT SUMMARY Approximately 3.1 million adolescents are diagnosed with depression each year with over 60% not receiving or engaging in mental health care. In an effort to address the significant challenges in access to and engagement with evidence-based psychosocial interventions (EBPIs) for adolescent depression, investigators in the University of Washington’s Departments of Psychiatry and Behavioral Sciences (MPI Jenness) and Human Centered Design and Engineering (MPI Kientz) partnered to conduct pilot work addressing these challenges through the use of Asynchronous Remote Communities (ARC) supported behavioral activation (BA+ARC). ARCs are technology-mediated groups that use private online platforms (e.g., Slack, Microsoft Teams) to deliver weekly tasks to participants and includes features such as asynchronous therapist and chatbot coaching, ecological momentary assessment (EMA) of mood, activity, and skill-use tracking, and peer communities that aim to improve support and motivation to engage in therapy and behavior change. Pilot work included successful design and development of a preliminary BA+ARC prototype (ActivaTeen) that was found to be acceptable, usable, and engaging to clinician and patient target users. The present proposal responds to PAR-21-131 “Pilot Effectiveness Trials for Treatment, Preventive and Services Interventions” and aims to advance this pilot work by conducting a mixed-methods study that 1) builds and conducts usability testing on a functional, usable, and robust BA+ARC platform that will satisfy the needs of mental health clinicians and adolescent patients identified through our pilot study (e.g., data security, HIPAA compliance, clinician workflow integration), and 2) tests the feasibility, usability, and change in proposed target mechanisms and outcomes of BA+ARC compared to BA treatment only (BA-Only) within a moderately-sized randomized control trial conducted within our partner site’s outpatient psychiatry clinic. We hypothesize 1) BA+ARC target users will report increased acceptability, feasibility, usability, and less burden than users of BA-Only; 2) BA+ARC adolescents will demonstrate improvements on hypothesized treatment mechanisms including therapist alliance, timeliness of intervention, social belongingness, and greater engagement in care compared to BA-Only adolescents; 3) Adolescents treated by BA+ARC versus BA+Only will have improved outcomes in depression symptoms and diagnoses and functional impairments. This research addresses the broader NIMH Strategic Plan Goal 4.3: Develop innovative service delivery models to dramatically improve the outcomes of mental health services received in diverse communities and populations by investigating a novel, technology-mediated service model that has the potential to improve access to and effectiveness of EBPIs for adolescent depression.