Objective: To report experimental impacts of a universal, integrated school-based intervention in social-emotional learning and literacy development on change over 1 school year in 3rd-grade children's social-emotional, behavioral, and academic outcomes. Method: This study employed a school-randomized, experimental design and included 942 3rd-grade children (49% boys; 45.6% Hispanic/Latino, 41.1% Black/African American, 4.7% non-Hispanic White, and 8.6% other racial/ethnic groups, including Asian, Pacific Islander, Native American) in 18 New York City public elementary schools. Data on children's social-cognitive processes (e.g., hostile attribution biases), behavioral symptomatology (e.g., conduct problems), and literacy skills and academic achievement (e.g., reading achievement) were collected in the fall and spring of 1 school year. Results: There were main effects of the 4Rs Program after 1 year on only 2 of the 13 outcomes examined. These include children's self-reports of hostile attributional biases (Cohen's d = 0.20) and depression (d = 0.24). As expected based on program and developmental theory, there were impacts of the intervention for those children identified by teachers at baseline with the highest levels of aggression (d = 0.32-0.59) on 4 other outcomes: children's self-reports of aggressive fantasies, teacher reports of academic skills, reading achievement scaled scores, and children's attendance. Conclusions: This report of effects of the 4Rs intervention on individual children across domains of functioning after 1 school year represents an important first step in establishing a better understanding of what is achievable by a schoolwide intervention such as the 4Rs in its earliest stages of unfolding. The first-year impacts, combined with our knowledge of sustained and expanded effects after a second year, provide evidence that this intervention may be initiating positive developmental cascades both in the general population of students and among those at highest behavioral risk. (Contains 4 tables and 3 figures.)