Making time for physical education doesn't hurt grades, and may help boost girls' test scores, according to a new study.

The report, written by Centers for Disease Control and Prevention scientists, addresses concerns of school administrators who fear that increasing P.E. time will interfere with pressure to raise standardized test scores. The study was released Thursday in the online version of the Journal of American Public Health.

The scientists, who specialize in obesity and school policies, examined standardized math and reading test scores from 5,000 students across the nation as they moved from kindergarten through fifth grade.

Girls who spent the most time in P.E. classes, from 70 to 300 minutes a week, had slightly higher test scores than girls who spent less than 35 minutes a week in the classes. There was no significant difference in academic achievement for boys.

The group is hoping that the study will convince educators trying to raise test scores that cutting P.E. isn't the answer, said Susan Carlson, the study's lead author and a CDC epidemiologist.

The issue crops up as public health workers and parents look for ways to curb the growing number of overweight children. The obesity rate for adolescents has tripled in the past three decades.

A bill introduced last week in the Georgia Senate (S.B. 506) would require school districts to comply with Department of Education regulations for physical education classes, which works out to about 30 minutes a day for elementary students.

Carlson said the scientists had several theories about why the most physically active girls had higher test scores, although no difference was seen among boys. The report called for further study of the discrepancy.