The Journal of School Health recently published a study that stated there was a significant relationship between fitness and academic achievement.  Children who exhibited fitness achievement (by passing fitness tests in PE class) increased their odds of passing the state English and math tests.

Reference:  Virginia R. Chomitz, Meghan M. Slining, Robert J. McGowan, Suzanne E. Mitchell, Glen F. Dawson, Karen A. Hacker

Is There a Relationship Between Physical Fitness and Academic Achievement? Positive Results From Public School Children in the Northeastern United States Journal of School Health: 79 (1) 30-37 2009.