There are more than 5 million youth in the U.S. with serious emotional disturbance (SED), defined as the presence of an emotional or behavioral disorder and functional impairment. Youth with SED have a prevalence of obesity that exceeds that of the general youth population, and youth mental illness has been identified as a risk factor for early cardiovascular disease; thus, addressing risk for overweight and obesity among youth with SED is critical. While behavioral lifestyle interventions for healthy weight are effective in the general population, these interventions do not typically address the influence of mental health symptoms on health behaviors. To address this gap, our team developed and tested CHAMPION, a tailored behavioral lifestyle intervention for youth with SED at risk for or with overweight/obesity, which was the first such intervention to demonstrate efficacy. To facilitate the integration of CHAMPION into treatment settings serving youth with SED, we propose to use the Enhanced Replicating Effective Programs (REP) framework, a multi-component strategy designed to translate evidence-based interventions into community settings. REP uses partner-engaged methods, with activities informed by a community working group comprised of potential intervention users (e.g., youth with SED and their families); implementers (staff who might deliver the intervention); adopters and sustainers (e.g., administrative leadership). We will work with three distinct types of mental health settings serving youth with SED (Psychosocial Rehabilitation Programs, Coordinated Specialty Care programs for early psychosis, and Therapeutic Day Schools). We propose to: 1) Adapt the CHAMPION intervention package to facilitate ease of delivery by diverse staff within a range of contexts serving youth with SED through a mixed methods usability evaluation with community working group members; 2) Refine multi-level implementation strategies for the sustained delivery of CHAMPION via a series of structured community working group meetings focused on refining and operationalizing the Enhanced REP strategies (e.g., defining activities included in Facilitation); and 3) Conduct an open pilot and mixed methods evaluation of the 6-month CHAMPION intervention package and selected implementation strategies in partnership with at least six sites, 24 implementing staff, and 60 youth. Primary outcomes will include: 1) session delivery and fidelity; 2) sites’ fidelity to the implementation intervention; 3) feasibility, acceptability, and appropriateness of the intervention package and implementation strategy to implementing staff; and 4) patient satisfaction with the intervention. Secondary outcomes will include youth BMI z-score, dietary behavior, physical activity, and behavioral functioning, implementation cost; and strategy mechanisms (provider self-efficacy and knowledge; organizational implementation climate and teamwork/relational coordination). This study will provide prelim...