PROJECT SUMMARY Youth in foster care have documented higher rates of substance use and unmet behavioral health needs than youth who are not involved in the child welfare system. Social determinants of health (e.g., child maltreatment, community violence) have been consistently identified as driving increased likelihood of substance use among foster youth and may also explain why those who use substances also experience high rates of co-occurring mental health needs. Access to substance use prevention interventions is sorely limited in part due to inadequate linkage between child welfare and behavioral health serving systems but also due to other factors such as stigma, lack of intervention options that include peers with lived experiences and lack of intervention tailoring to unique needs. Behavioral intervention technologies (BITs) hold great promise to increase access to youth substance use prevention interventions. Participatory technology co-design approaches allow for foster youth to tailor technology interventions to their relevant multiple social and contextual drivers of health vulnerability and inherently reduce stigma and build youth engagement because peers with lived experience drive BIT design and content. FostrSpace is a BIT co-designed with foster youth that provides tailored substance use prevention resources, services navigation, direct peer supports and direct in-app access to evidence-based substance use and mental health (SU/MH) interventions. To promote successful uptake and utilization of stand-alone technology for underserved populations such as Fostrspace, however, research indicates additional systems and structural level intervention is required. Court Appointed Special Advocates (CASA) are community volunteers who support and advocate for the needs of abused and/or neglected children and who hold promise as facilitators for foster youth SU/MH services referrals. Evidence-based telementoring and training models such as Extension for Community Health Outcomes (ECHO) have been highlighted as a crucial strategy for expanding SU/MH services access. This study, in partnership with California CASA programs, will study ECHO's effectiveness as an implementation strategy to facilitate FostrSpace referrals from CASA volunteers and assess FostrSpace's reach and effectiveness in preventing SU among foster youth. RE- AIM (Reach Effectiveness-Adoption Implementation Maintenance) and PRISM (Practical Robust Implementation and Sustainability Model) frameworks guide aims. The R61 phase (Planning/Exploratory) will include peer and CASA co-design meetings for implementation strategy (ECHO) and intervention (FostrSpace) adaptation, open trial and R33 trial planning. The Hybrid II R33 trial mixed-methods design will test effectiveness of FostrSpace in preventing progression of youth substance use and effectiveness of ECHO as implementation strategy to increase reach of FostrSpace through CASA programs using a cluster randomized controlled trial design comparing ECHO-FostrSpace to standard referral practice with 400 youth and 400 CASA volunteers across 10 CASA programs.

PROJECT NARRATIVE Substance use and co-occurring mental health concerns continue to be a major public health concern among youth in the foster care system making access to substance use prevention services a key priority. Digital behavioral health technologies have the potential to rapidly and efficiently increase access to prevention resources and interventions, but linkage to such available technologies requires facilitation by systems already serving these youth. The proposed Hybrid II mixed methods study will evaluate implementation effectiveness of a telementoring program with Court Appointed Special Advocates (CASA) to increase foster youth referrals to a digital behavioral health app (FostrSpace) and determine FostrSpace's effectiveness in preventing youth substance use.