Study co-author Trent A. Petrie, director of the Center for Sport Psychology at the University of North Texas, and colleagues gathered data at five Texas middle schools from 1,211 students, of whom 54 percent were female -- with an average age of about 12. Overall, the group was 57 percent white.
"Cardiorespiratory fitness was the only factor that we consistently found to have an impact on both boys' and girls' grades on reading and math tests," Petrie said in a statement. "This provides more evidence that schools need to re-examine any policies that have limited students' involvement in physical education classes."
For girls, having a larger body mass index was the only factor other than cardiorespiratory fitness that predicted better reading scores. However, for boys and girls, cardiorespiratory fitness was the only factor related to their performance on the math tests, Petrie said.
"The finding that a larger body mass index for girls was related to better performance on the reading exam may seem counterintuitive, however past studies have found being overweight was not as important for understanding boys and girls performances on tests as was their level of physical fitness," Petrie said.
The findings were presented at the American Psychological Association's 120th annual convention in Orlando.