Iron and zinc are important micronutrients for cognitive development and growth in children, particularly during infancy when brain development and physical growth are rapid. Iron and zinc deficiencies likely coexist in young children in poor developing countries due to high requirements for these micronutrients at this age, low consumption of animal products (which are rich sources of these nutrients) and similar problems of poor bioavailability from plant foods. One would expect that iron and zinc supplementation in infancy would be an appropriate strategy to promote long-term cognitive development and school achievement, but this has never been evaluated. We have many studies of the effects on micronutrient interventions in infancy but the benefits of these interventions have been assessed only in terms of outcomes in infancy. What are missing are studies of micronutrient interventions during the critical phase of infancy that report effects measured in school children and beyond. Only then will we begin to understand the full impact of micronutrient interventions in infancy on human function. From 1998 to 1999, a randomized, placebo controlled trial of iron and zinc supplementation was carried out in 609 4-6 month-old infants in Khon Kaen province, Thailand. Infants were randomized to four groups (zinc, iron, iron and zinc, placebo) and those supplemented received 10 mg of iron and/or 10 mg of zinc daily for 6 months. Improvements in iron and zinc status and in ponderal growth were found; no measures of cognitive development in infancy were included. We propose a follow-up study of these children at ages 8 to 10 years. From February to July 2006, we conducted a pilot study and were able to locate 584 or 96% of the sample. The children are all in school and we propose to assess schooling, cognitive performance (Wechsler test adapted to Thailand) and language and mathematical skills. In addition, data on physical growth, biochemical status, dietary intakes and socioeconomic status will be collected. We expect that knowledge from this study will be useful for properly assessing the full benefits of improving iron and zinc status in early childhood.