Zinc, a mineral essential for growth, development and immune function, may help adolescents do better in school. In a 10-week study, more than 200 seventh-graders drank fruit juice supplemented with zinc, took various cognitive tests such as visual memory and word recognition and performed tasks that required attention and vigilance. Those who drank the zinc-supplemented juice scored better than those who had the regular juice. However, test performance did not improve significantly among kids who already met the recommended daily allowance for zinc. Researchers say these results may prompt a review of the recommended intake guidelines for adolescents because the teen years are a time of rapid growth and development. Good food sources of zinc include red meats, poultry, beans, nuts, whole grains and some seafood.