Abstract/Summary In response to the public health threat that suicide poses to American youth in general and incarcerated youth in particular, we propose a multi-year, multi-site, setting-level intervention in the New York City Juvenile Justice system. In partnership with the NYC Administration for Children's Services (ACS), we will experimentally evaluate an evidence-based staff-level training (S4L) to address youth suicidality during two critical points of contact for juvenile-justice involved youth: placement and post-release Aftercare. S4L combines training in Shield of Care (SOC), an evidence-based model for acute suicide detection training for juvenile justice staff, with evidence-based suicide prevention skill-building training informed by dialectical-behavior therapy for adolescents at risk for suicide ideation, behavior, and non-suicidal self-injury (NSSI). We will compare the effectiveness of S4L to a training as usual control condition (control), and to a condition in which we provide monthly on-site coaching to staff to support the acquisition and implementation of S4L skills (S4L+). The intervention will be implemented as part of ACS's usual staff-training procedures. The need for intervention is urgent at this time due to recent state-level policy shifts that will increase the number youth in these sites and heighten their suicide risk. S4L and S4L+ will be evaluated using a 3-arm cluster-randomized design with the full population of non-secure placement (NSP)/Aftercare sites (N=30 sites; N=1800 youth, 30% girls). These sites are sole infrastructure for long-term confinement in NYC. NSP/Aftercare sites will be randomized to control (N=10 sites; 600 youth), S4L (N=10 sites; 600 youth), and S4L+ (N=10 sites; 600 youth) conditions. We test the effectiveness of S4L compared to S4L+ and control on improving suicidal behavior, suicidal ideation, and NSSI; mental health outcomes (internalizing, externalizing and substance use); and correlates of suicide/mental health (impulsivity, mood, and coping). In addition, we test the extent to which site-level implementation characteristics (e.g., proportion of staff trained; average amount of detection and prevention activities); site and staff-level structural characteristics (e.g., prior training, burnout); and individual youth characteristics (e.g., demographics; trauma history) moderate S4L and S4L+ effectiveness. Youth outcome data on suicidal behavior, suicidal ideation, NSSI, and mental health problems and their correlates will be tracked longitudinally for 1 year. In response to the FOA, outcomes will be assessed via evidence-based measures that capture dimensional facets of disorder in line with NIH's common data elements and recommendations by the National Action Alliance for Suicide Prevention. Site-level intervention moderators will be measured by staff survey and administrative data. This project aims to expand the scientific knowledge base on suicide prevention and intervention in hig...