Objective: Adverse childhood experiences are linked with poorer physical, social, and psychological well-being, especially for individuals who live in poverty. As adverse childhood experiences accumulate, risk for poor outcomes increases. Therefore, it is imperative that preschools and elementary schools are equipped to prevent and intervene upon traumatic stress. Trauma Smart is an organizational change intervention designed to build trauma-informed knowledge, attitudes, skills, and resources within schools serving young children. Method: The current study evaluates the effectiveness of Trauma Smart staff training in 42 preschools and elementary schools with 2,418 staff using a 1-year, longitudinal, prepost design. Trauma Smart implementation occurred during scale-up, under real world conditions. Satisfaction, posttraining knowledge about trauma-informed approaches, and pre-to-posttraining changes in attitudes favorable to trauma-informed care were evaluated. Results: As hypothesized, staff were highly satisfied with the training (mean ratings indicate 92% satisfied), demonstrated knowledge of core concepts related to trauma-informed care (mean quiz scores were scored 90% correct), and developed more favorable attitudes toward trauma-informed care following training, with medium-large effect sizes. Conclusions: Trauma Smart staff training is feasible, acceptable, and has the potential to improve the knowledge and attitudes relevant to trauma-informed approaches within preschool and elementary school staff, including those who serve children who live in poverty. (PsycInfo Database Record (c) 2021 APA, all rights reserved).