Introduction: Minority and low-income children are underrepresented in school-based weight management programs despite higher risk of obesity and the external contexts that influence their success are largely unknown. This study examines predictors of weight outcomes following the socioecological model in a school-based weight management intervention implemented in an elementary school serving primarily low-income, Black youth. Methods: Children (n = 145; ages 4-9) participated in an 8-month school-based weight management intervention that included components to increase physical activity, promote healthy eating, and engage parents. Children had height and weight measured at baseline and postprogram and parents completed questionnaires at baseline. Socioecological predictors (e.g., child demographic, parent beliefs and attitudes, family and home environment, and social contexts of the family) of zBMI change were assessed using linear regressions. Results: Weight change over the program differed by baseline weight status such that children with obesity lost weight, while children of healthy weight and with overweight gained weight. Children who were younger and had healthier family food choices at baseline were better able to maintain their weight, whereas children from food insecure families gained weight. Discussion: Children of different weight categories from low-income families vary in their response to universally delivered school-based weight management programs. Future work should consider how to address needs of children from different weight classes as well as to effectively target children with risk factors for excessive weight gain (e.g., older, food insecure, less healthful food choices), which may involve broader or more integrative approaches. (PsycInfo Database Record (c) 2021 APA, all rights reserved).