Advancing Health Equity through Park Afterschool Programs - Abstract Youth in systemically marginalized communities have disproportionately high rates of mental health need and low rates of service utilization [1,2]. Afterschool programs (ASPs) promote positive youth trajectories in communities impacted by systemic inequities.[39] High quality ASPs rely on youth-adult relationships and well- organized routines to build social-emotional skills[44-46] commonly targeted in evidence-based prevention programs. For decades, investigators have tried to bring school-based programs to ASPs[51,52] via traditional teacher training for manualized curriculum delivered in structured lessons. There are two problems with this model for ASP: 1. Staff and youth dislike the school-like format of big, complex curriculum; also, kids in ASPs arrive late and leave early, and miss instruction that’s offered only during specific structured time; 2. Common one-and-done in-person teacher professional development workshops do not transfer well to ASP providers, and the one-size-fits-all approach neglects their diverse education, training, and experience. Frequently changing schedules, priorities, and resources among ASP make rigid adherence to manualized programs unlikely and unsustainable. Professional Development in ASPs must: (1) provide differentiated instruction and culture- and context-based application of knowledge; (2) include ongoing support for knowledge action; and (3) be responsive to organizational- and provider-level influences on knowledge action and outcomes. This R01 application extends collaboration with a national advisory board and three large urban county park districts (LA, Chicago, Miami), and proposes a mixed method, multi-site, transportability research design to examine organizational- and provider-level facilitators and barriers to knowledge action. ASP providers (n=180, ~55% female, 40% White, 45% Black/African American, 5% Asian American, 10% multiracial, 30% Hispanic/LatinX) will receive professional development emphasizing tools and teachable moments related to emotional insight and regulation. Participants will self-select the formats and frequency of ongoing support for the duration of an ASP session (~3-4 months) from: (a) ongoing access to online training; (b) “nudges” via SMS text messages; and (c) facilitated discussion with expert or peers during monthly Zoom coffee hours. Pre- and post- surveys, and weekly check-ins, will assess provider knowledge, self-efficacy, attitudes, infusion of learned content into ASP programming and well-being. Randomly selected providers (n=15 from each park district) will participate in ~1-hour post-test interviews. Quantitative analyses will test predicted associations among knowledge consumption, knowledge action, and provider well-being and relationships with youth. Mixed method analyses will examine organizational- and provider-level facilitators and barriers to using and infusing social-emotional skills into natural ASP routines, and the quantity and quality of skills infusion necessary to positively influence provider reports of well-being and relationships with youth.