Background: In Brazil, iron deficiency anemia is considered a public health problem, which has a direct impact on the process of child growth and development. To assess the impact of a powdered supplement added to food preparations, on hemoglobin (Hb) levels and other hematimetric parameters in children. Method: This study is a double-blind, community-controlled clinical trial conducted in education centers in the northeast of Brazil. In this trial, food preparations were offered with a powdered supplement, enriched with iron (intervention) and control (no supplementation), Monday through Friday, for 60 days. Two biochemical evaluations were performed to determine Hb, hematocrit (Ht), mean corpuscular volume and ferritin levels before and after the intervention. Results: For participants in the 6- to 59-month age range, we identified an increase in mean Hb concentrations and other hematimetric parameters. In the 5- to 11-year age group, there was a significant increase in both groups for Hb and Ht values, and mean Hb concentration was significantly greater in the intervention group (12.25±0.76 vs. 11.93±0.94, p<.0035). In the 12- to 14-year-olds, all variables analyzed presented an increase. Conclusions: This school-based intervention effectively increased Hb concentrations other hematimetric parameters and reduced the prevalence of anemia in children and adolescents.