This randomized controlled trial examined the efficacy of an elementary school service-learning program, Connect Science (CS), on classroom practices and students' science achievement, civic engagement, and social skills. Fourth grade teachers were enrolled into intervention versus control conditions resulting in 41 classrooms (20 intervention) with 868 students (423 intervention). Intervention group teachers taught CS and control group teachers taught "business-as-usual" science over a 14-22 week period. CS had a positive impact on classroom practices (Next Generation Science Standards and CS practices). Analyses showed positive impact of CS on science achievement and energy attitudes and behaviors. Use of CS practices mediated the relation between CS and energy attitudes and behaviors. Improved social skills were evident in conditions of high fidelity of implementation. [This is the online version of an article published in "Journal of Applied Developmental Psychology."]