A new study suggests one explanation for why girls do better in school than boys: sleep cycles.

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The decision by several area school districts, including Seattle, to delay start times for high-school classes has been touted as a positive move that better matches teens’ biological clocks and helps them learn better.

Now a new study suggests that later start times may have a particular benefit for boys.

Researchers from the University of California, Davis looked at scores from a six-year experiment involving middle and high schools in Eastern Europe where students’ classes alternated every month between starting at 7:30 a.m. and 1:30 p.m. The boys’ test performance increased more in afternoon classes. Their scores, on average, didn’t reach or surpass the girls’ scores, but that the gap between the scores shrank by 16 percent.

Girls are better at sitting still for several hours, one of several factors that also may explain why they outperform boys in school. The UC Davis researchers say their study adds a new one: sleep cycles. Boys have longer “body clocks,” resulting in later bedtimes and wake-ups. Girls also spend more time in “deep sleep,” which helps boost memory.

“If boys receive less sleep than girls and are particularly harmed by lack of sleep, then early school start times could help explain settings where girls outperform boys,” the researchers wrote in the study.

Seattle is one of the largest school districts in the nation that is changing its start times. This fall, high schools and most middle-school classes will begin at 8:45 a.m.

A number of nearby districts are doing the same, including Bellevue, where high-school classes will start between 8:15 and 8:30 a.m. In Mercer Island, the high school will start class at 8:45 a.m. on Wednesdays and 8 a.m. the rest of the week.