Childhood overweight has increased significantly in the past 20 years, with the highest rates noted among Mexican Americans. Schools are an optimal setting for intervention efforts; however, few programs have demonstrated actual decreases in weight. This study evaluated an intensive school-based program designed to result in weight reduction for overweight Mexican American children. A total of 71 children (32 males, 48%) between the ages of 10 and 14 at or above the 85th percentile for body mass index (BMI) were randomized into a six-month intensive intervention (II) or self-help (SH) condition. Results revealed that children in the II condition significantly reduced their standardized BMI (zBMI) when compared with the children in the self-help condition (F(2,62)=6.58, p=0.003). The change in zBMI was significantly different at both 3 and 6 months (F(1,63)=5.74, p=0.019, F(1,63)=12.61, p=0.001, respectively) with II participants showing greater decreases in weight. The 3-month change in zBMI for the II participants was a decrease of 0.07 compared with a decrease of 0.01 for SH participants. The 6-month change in zBMI was a decrease of 0.11 for II and an increase of 0.03 for SH. Overall, the results are promising, suggesting that an intensive school-based intervention may be an effective means for promoting weight loss in overweight Mexican American children.