PROJECT SUMMARY/ABSTRACT Pediatric obesity contributes to life-long chronic diseases and shortened life expectancy, making it a public health priority. Rural children have disproportionately higher rates of overweight/obesity compared to their urban coun- terparts and have limited access to treatment options. Even when participating in a treatment intervention created from expert guidelines, up to 76% of participants may not be successful at maintaining or reducing their body mass index z-score (BMIz). It is critical that we have treatment programs that are effective for individuals and are easily delivered and adopted to rural areas. Therefore, the objective of the current study is to understand factors specific to rural populations that are related to success of pediatric obesity interventions at both the individual and site (school)-level. This will be done through rigorously applying the RE-AIM framework, which examines both individual effectiveness and intervention implementation, to a pediatric obesity treatment inter- vention. We will accomplish this through two unique aims; Aim 1 will investigate two novel individual-level pre- dictors, engagement and change in sedentary behavior, on treatment success (reducing BMIz). This aim will use data collected from intervention arms of two randomized pediatric obesity clinical trials (N = 105) in rural areas conducted by Dr. Davis (primary sponsor). The intervention included group-sessions that were video recorded; these videos will be coded for our application of a novel measure of engagement, the Group Engagement Meas- ure. Additionally, we will analyze change in sedentary behavior (collected at both baseline and post intervention). Engagement and change in sedentary behavior will be added into a model with typical predictors of participant success; the new model is expected to predict success better than a model using only typical predictors. Aim 2 will systematically identify site (school)-level contextual factors, including barriers and facilitators, and test their associations with successful site-level implementation. To address Aim 2, we will invite site (school) represent- atives to participate in a semi-structured interview to understand barriers and facilitators associated with suc- cessful implementation. Representatives will fall into one of three categories based on adoption of the interven- tion at their site: 1) did not adopt 2) initially adopted or 3) adopted the intervention. Training goals for this study are to: 1) develop and apply strategic skills related to intervention and implementation research designs and methodology (clinical trials, implementation science, qualitative methods and behavioral coding), 2) advance training in energy balance, including sedentary behavior analysis and nutritional measurement methods and analyses , 3) advance statistical skills for multi-level modeling, and 4) enhance professional development skills in scientific writing and presenting research...