Ask a group of grade school students to name their favorite class and the overwhelming and immediate response is “recess!” Kids are not wired to sit still for hours focused on learning math equations or memorizing facts. They’re built to move and need the time in their day to unplug their brain and restart their legs.

However, school administrators and teachers are facing growing pressure to reduce this play time in favor of more instruction time to meet tougher academic standards. Two new research studies argue that would be counterproductive showing that exercise and aerobic fitness are key contributors to cognitive performance.

According to the Harvard University School of Public Health

, 1 out of 3 U.S. children are overweight or obese, which is triple the rate of 1963. In Europe, about 25% of school-age kids were also at an above normal weight. Certainly, diet and nutrition play a role but a 2007 Robert Wood Johnson Foundation study

reported that only 36% of kids get the recommended one hour of physical activity per day. Recess represented the best chance for students to fit exercise into their daily schedule, accounting for almost half of the “opportunity time” in a child’s day.

University of Illinois researchers Charles Hillman, professor of kinesiology, and Arthur Kramer, professor of psychology, have both been studying the effects of exercise on academic performance for over a decade. Their team’s latest research, published last week in PLoS One, compared the learning skills of 48 kids, age 9-10. First, they tested the aerobic fitness of all the students on a treadmill and divided them equally into a “high fit” group and a “low fit” group.

Next, the students were shown a map of a fictitious country with different regions drawn, each with a made-up name, and asked to memorize them. After the initial learning session, there was no difference between the two groups. However, after a one day retention period, they were tested again and the high fit students were able to name 40 percent of the regions correctly while the low fit group could only answer 25 percent correctly.

“Fitness can boost learning and memory of children and these fitness-associated performance benefits are largest in conditions in which initial learning is the most challenging,” wrote the researchers.

Given the small sample size of the Illinois study, some may not be convinced of the link between fitness and grades. Dr. Robert Rauner

of the Partnership for Healthy Lincoln teamed up with the Lincoln, NE public school district to compile a massive study of almost 12,000 students, published last month in the Journal of Pediatrics. The results of each student’s time on a fitness shuttle run called PACER (Fitnessgram's Progressive Aerobic Cardiovascular Endurance Run) were compared with their performance on the Nebraska State Accountability (NeSA) math and reading tests, the standardized tests required of all students in the state.

Those students classified as aerobically fit by their PACER test results were 2.4 times more likely to pass the math tests and 2.2 times more likely to pass the reading tests than students who were not fit aerobically.

The results delivered a clear signal for school administrators.

"Schools sacrificing physical education and physical activity time in search of more seat time for math and reading instruction could potentially be pursuing a counterproductive approach," said Dr. Rauner.

Whether its recess time at school or organized youth sports, the message is clear that kids who exercise grow their muscles and their brain.