Project Summary/Abstract (30 lines) In the United States, 15 million children and adolescents need psychological services; yet only one-third receive psychological services of any kind. Even fewer receive care that is consistent with evidence-based guidelines for best practices. This gap has widened dramatically with the negative effects of the COVID-19 pandemic on the mental health of children, combined with disruptions to school-based mental health services. Mental Health Apps (MHapps) show early promise to alleviate mild to moderate forms of emotional disorders like anxiety and depression, while improving broader domains of functioning, including academic engagement and social competence. These MHapps are designed to promote youth mental health by delivering targeted, skills-based curricula in an interactive and accessible format. Unfortunately, the potential for MHapps has thus far been limited by low engagement, improper use, and high rates of noncompletion. Caring adults can help boost youth engagement in MHapps through what behavioral scientists refer to as “supportive accountability”—that is, regular check-ins, monitoring, troubleshooting, and other interactions. Several studies have highlighted the positive associations between supportive accountability and user engagement, number of logins, use of interactive tools, and outcomes. In fact, they have shown that, with guidance, the effects of technology-delivered interventions are comparable to those obtained in face-to-face interventions. By contrast, self-guided programs have yielded relatively fewer benefits. Moreover, the studies have found no difference in outcomes when youth were supported by clinicians versus everyday caring adults. Based on evidence that effectiveness and adherence to eHealth interventions is enhanced by human support, we developed a software framework (MentorHub) that coordinates the deployment and monitors the use of evidence-based MHapps. We anticipate that MentorHub will be widely used in youth-serving organizations (e.g., youth mentoring programs) and school based settings (e.g., secondary and post-secondary schools). The proposed research in Phase I will further (Aim 1) refine the MentorHub Product to establish usability (UI/UX) and feasibility in a large, youth mentoring program; and (Aim 2) determine the impact of the Product on youth mental health outcomes (transdiagnostic indicators of risk for mental illness, internalizing and externalizing symptomatology, and broader indicators of youth functioning). The pilot RCT study will test the short-term efficacy of the product in a national youth mentoring organization (Big Brothers Big Sisters New York) and involve 300 participants (75 mentor-mentee pairs/dyads randomized to the test group and 75 mentor-mentee pairs/dyads randomized to the control group). By the end of Phase I, we will have a tested product ready for national testing across Big Brother Big Sisters locations and in new school-based settings. By ...