In a group randomized trial of 45 elementary schools, a whole-child health and wellness curriculum introduced as a regular part of the educational programming was compared to education as usual over 2 years with a 2-year follow-up. The curriculum focused on integrating multiple SEL skills--mindfulness, compassion, and physical awareness--with the intent to advantage developmental patterns for these skills, academic engagement, personal well-being, and student behavior. The program design and trial implementation were launched with end-use delivery and long-term sustainability as integral considerations. Effects were shown for several SEL skills and behavioral indicators previously robustly correlated to long-term outcomes. Effects were demonstrated more broadly in schools serving high-poverty communities, suggesting the impact was stronger where the need was greater. Results are interpreted regarding supporting school-based SEL, the potential of applying group randomized trials with end-use conditions of implementation, and the value of fitting innovation efforts to school system operations, mandates, and priorities for promoting sustainability.