Background: To evaluate the effect on problem behaviors of a universal school-based prevention curriculum of third grade students. Methods: Six regular classes in 1 elementary school were randomly assigned to an intervention (n = 208) or control (n = 209) group. A 13-session program was offered to students in the intervention group. The Achenbach Child Behavior Checklist (CBCL), parent report, was used to assess problem behaviors at baseline, at the conclusion of the curriculum, and again at 6-month follow up. Results: The unadjusted mean estimates of behavioral problems were significantly lower in the intervention group posttest (at the conclusion of the curriculum), -3.53 (95% confidence interval [CI] = -6.59 to -0.48; p = 0.023) and at the 6-month follow up, -5.22 (95% CI: -8.27 to -2.16; p = 0.001). After adjusting for potential confounders, gender (female), father's educational status (high school), family relationships (good and average), and child's age in months, intervention groups (intervention posttest and intervention after 6-month follow up) showed significantly lower total behavioral scores. Conclusions: A universal school-based prevention program for Chinese elementary school-age children resulted in a significant positive change in behavioral problems. This is an important finding in the context of the Chinese 1-child policy that places great value on the achievement of the child. (Contains 1 figure and 5 tables.)