Children who participate in sports teams or who get two hours of PE each day do better. The activity level must be vigorous. Minimal to moderate levels of physical activity and exercise aren't enough to influence a student's grades.

Scientists think there are several reasons for this effect. First, increased activity at a level described as 'vigorous' increases arousal and may reduce boredom. The result is an increased attention span and better ability to concentrate.

Self-esteem may be improved with increased levels of activity. Improved classroom behavior is a natural outcome of improved self-esteem.

Researchers suggest there may be a threshold level required to induce arousal and other desirable effects. Further studies are needed to find out just exactly how much exercise is needed to make a difference.