I'll bet this also applies to middle-age adults and senior citizens:
Last month, Harvard researchers reported in The Journal of School Health that the more physical fitness tests children passed, the better they did on academic tests. The study, of 1,800 middle school students, suggests that children can benefit academically from physical activity during gym class and recess.
A small study of children with attention deficit hyperactivity disorder last year found that walks outdoors appeared to improve scores on tests of attention and concentration. Notably, children who took walks in natural settings did better than those who walked in urban areas, according to the report, published online in August in The Journal of Attention Disorders. The researchers found that a dose of nature worked as well as a dose of medication to improve concentration, or even better.