Suicide is the second leading cause of death in those aged 10 to 19 years; it is a critical public health problem. Suicidal ideation and nonfatal suicide attempts are even more prevalent and result in substantial morbidity and increased risk of suicide. Pediatric primary care is an ideal service setting for intervention research designed to rapidly reduce suicide and suicidal behaviors among US youth, as 80% of youth who die by suicide are seen by their primary care clinicians (PCC) in the year prior to death while only 20% have contact with a mental health professional. Despite the importance of identifying youth at risk for suicidal behavior, most PCCs do not routinely screen for suicide. In recent years, new treatment and management strategies have been developed, tested and implemented in some organizations, but they are not yet widely used. Existing clinical trials have tended to focus on testing effectiveness of evidenced-based interventions (e.g., universal screening, safety planning) for high-risk populations in emergency departments; less is known about the efficacy of these approaches in primary care settings. Research is critically needed to test the effectiveness of evidence-informed practices to reduce suicide risk for youth treated in primary care. To address this gap, we propose a stepped wedge hybrid effectiveness-implementation cluster-randomized controlled trial to test effectiveness of a population-based quality improvement (QI) intervention, Stepped Approach to Reducing Suicide in Primary Care (STARRS_PC) that implements a clinical pathway for youth identified by screening as being at elevated risk for suicide. The pathway is designed to promote the use of evidence-based suicide clinical care processes and includes three separate components: suicide risk screening, risk assessment and triage, and care management. The application builds on a pilot study of real- world implementation of suicide risk screening into a pediatric primary care setting, using an iterative Plan, Do, Study, Act (PDSA) quality improvement approach that was well-accepted by patients, families, and PCCs. In the proposed study, we will test the effectiveness of STARRS-PC relative to treatment as usual (TAU) on primary (suicidal attempts and suicide deaths), secondary outcomes (suicidal ideation, non-suicidal self-injury, and family satisfaction) at 3, 6, 12 months post-baseline; examine clinicians’ knowledge, self-efficacy, and buy- in regarding suicide risk screening, assessment, and management as mechanisms of change; and organizational factors (e.g., organizational readiness and practice integrations) as potential moderators of the treatment effect on patient outcomes During this five-year project, we will recruit and assess 2274 youth aged 12 to 17 years from 12 primary care sites, including 910 youths during the TAU phase and 1364 youths during the Screening + Intervention phase. Participating sites serve vulnerable low-income youth in urban and rura...