A study by a University of Iowa economist finds that increased physical education requirements help reduce obesity among fifth grade boys, but fifth grade girls showed little change.

Childhood obesity has risen dramatically in recent decades, prompting public health officials and policy makers to advocate increased physical activity time for elementary school children. In response, many state legislatures have mandated students take a minimum number of hours of physical education in school to increase their activity and introduce them to better fitness habits.

A study co-authored by David Frisvold, assistant professor of economics in the Tippie College of Business, is one of the first to examine how states’ physical education requirements affect childhood obesity in elementary school. The study uses data from the Early Childhood Longitudinal Study, a survey of thousands of students annually. One item it measures is Body Mass Index (BMI), and Frisvold’s study uses the BMI of students who entered kindergarten in fall 1998.

The survey also recorded physical activity by measuring how much time the students spent in physical education classes; and it surveyed parents and teachers to measure how often children participated in physical activity outside of PE class and how much time they spent watching TV.

Finally, the study gathered data on PE mandates in each state and how students in the longitudinal survey fared in light of their state’s mandate.

In the end, Frisvold’s model estimates that an additional 60 minutes per week of mandated PE class would lower BMI by 10 percent among fifth graders, reducing the probability of youth obesity by 5 percentage points.

However, that benefit was focused almost entirely on boys, as the effect on fifth grade girls was essentially zero. Frisvold’s study suggests that girls may spend less time in physical activity and more time watching TV after school, but also speculates that boys may be more active during PE class than girls, or that PE teachers may structure different activities for girls than boys, or demand more of boys.

The study also suggests that school districts are not enforcing state mandated physical education requirements, such that only 34 percent of the students were in PE class for the amount of time their state requires. Only 17 percent of kindergartners spent the number of minutes in PE class required by their state, the study suggests, and only 45 percent of fifth graders did.

Frisvold said that when a state mandates 100 minutes of PE time, it translates into an actual increase of only 13 minutes for kindergartners and 40 minutes for fifth graders.

“Less than perfect compliance by schools reduces the power of state mandates to affect individual student PE time,” the study says.

States and school districts often say they reduce PE classes because they need more time teaching subjects that appear on standardized tests, such as those mandated by the federal No Child Left Behind law. But Frisvold’s study found that increased PE time had no impact on the amount of time spent studying academic subjects.

“Instead of schools cutting academic classes when PE mandates are increased, they seem to increase the length of the school day,” he says.

Frisvold’s study, “The Impact of Physical Education on Obesity Among Elementary School Children,” was co-authored by John Cawley of Cornell University and Chad Meyerhoefer of Lehigh University, and published by the Journal of Health Economics.