In 2004, Bogotá's Secretary of Education initiated a school snack program in public primary schools. A mid‐morning food ration was provided free of charge to children in order to supplement 30% and 50% of their daily requirements of energy and iron. To examine whether the snack program improved children's nutritional status, we conducted a longitudinal study of 3202 children ages 5‐12 y measuring micronutrient levels, anthropometry, and reported morbidity. After adjusting for socioeconomic status and other school interventions, children receiving the snack (SN, n=1803) had greater increases in plasma vitamin B12 (17 pmol/L; P<0.0001), ferritin (2.2 ug/L; P=0.02), and hemoglobin (0.1 g/L, P=0.05) after 3 months than children not receiving the snack (NOSN, n=1399). SN children reported significantly fewer days with morbidity symptoms (e.g. cough with fever, diarrhea with vomiting) and 37% fewer doctor visits (p=0.04) during the school year than NOSN children. There were no effects on height or BMI. Compliance with the snack was high, with more than half of the ration consumed on 94% of the days. Improvements in children's iron stores and vitamin B12 status with a school snack are encouraging; continued monitoring of its effect on ponderal growth is warranted as the rates of child overweight are increasing in Colombia. Funding: Bogota's Secretary of Education, Harvard DRCLAS, National Univ of Colombia, Colombian NIH