Several researchers have been making the case that aerobic exercise improves not only a student's fitness level, but also their test scores.

The federal No Child Left Behind program encourages schools to focus more of the school day on the core academic subjects while reducing class time in peripheral subjects, like art, music, and physical education. Only 6 percent of American high schools now offer a daily gym class. In his latest book, "Spark: The Revolutionary New Science of Exercise and the Brain," Harvard professor John Ratey argues for more physical fitness for students -- as a cure for not only their obesity but also their academic performance.

Exercise stimulates gray matter to produce brain-derived neurotropic factor, or BDNF. BDNF helps new neurons and their connections grow. In addition, levels of other neurotransmitters are increased after a strenuous exercise session.

Research showing a link between fitness and academics is growing. The California Department of Education found that kids who were fit scored twice as well on academic tests. Charles Hillman, a professor of kinesiology at the University of Illinois, was able to duplicate these findings with more than 250 third and fifth-grade students.