The role of zinc in children's cognitive and motor functioning is usually assessed by the response to supplementation in populations thought to be zinc deficient. A review of published zinc-supplementation trials that examined behavior and development identified one trial in fetuses, six trials in infants and toddlers and three trials in school-age children. The three studies that examined activity reported that zinc supplementation was associated with more activity. Of the five studies that examined motor development in infants and toddlers, one found improvements among very low-birth-weight infants, one found improvements in the quality of motor development and three found no impact. Of the four studies that examined mental development in infants and toddlers, three found no impact of zinc supplementation and one found that zinc-supplemented children had lower scores than control children. Among school-age children, one study found no impact of zinc supplementation on cognitive performance and two found a beneficial impact of neuropsychological processes, specifically reasoning. The evidence linking zinc deficiency to children's cognitive and motor functioning suggests a relationship among the most vulnerable children but lacks a clear consensus, highlighting the need for additional research into the timing of zinc deficiency and the co-occurrence with other micronutrient deficiencies.