Project Summary Obesity in childhood is associated with adverse cardio-metabolic outcomes as well as near-term adverse outcomes, including both physical and psychosocial morbidities. Evidence has shown that improving a child's body mass index (BMI) can lead to a more favorable cardio-metabolic risk profile and prevent adult obesity. However, many clinically-based randomized controlled trials (RCT) to improve a child's BMI have had limited success. Previous trials have used multiple concurrent components to achieve improved BMI status, making it difficult to know which components were effective. Identifying the most effective components of an intervention has been recognized by the USPSTF as a major gap in current research. One underused strategy to improve interventions is to study children in obesity RCTs who have succeeded in decreasing their BMI z-score by ≥0.2 units, hereafter referred to as “positive outliers.” During this 4 year K23 career development award, Dr. Fiechtner will leverage data from two randomized controlled trials for childhood obesity (STAR N=549 and Connect for Health = 721) to 1) identify which components of a childhood obesity intervention are most effective (Aim 1) 2) qualitatively engage parent stakeholders to examine in a detailed manner how their children achieved success or did not respond and how these lessons may be applied to others in similar neighborhood contexts (Aim 2); and 3) conduct a pilot study to prospectively test the identified effective components and strategies in a high-risk population tailoring the intervention to their neighborhood (Aim 3). Through this training plan she will expand upon a foundation of pediatric gastroenterology, nutrition, epidemiology and basic biostatistics to develop expertise in 1) advanced biostatics 2) qualitative methods 3) time series analysis 4) improvement/implementation science and 5) the practical skills necessary to lead a research team. She will leverage the wealth of resources of Massachusetts General Hospital, Harvard and the Institute for Healthcare Improvement to conduct the proposed analyses. These studies and trainings will lay the necessary scientific framework to launch her career as an independent physician scientist with the long-term goal of creating targeted effective interventions for particularly high-risk groups who are unable to get to a healthier weight, i.e. those where the “deck is stacked” against them because of cultural or environmental barriers. This proposal addresses NICHD's mission to ensure all children have the chance to achieve their full potential for healthy and productive lives.