For much of history, of course, most girls couldn’t even get a decent education. But as soon as girls joined the classroom, they revved ahead. These charts from the Organization for Economic Cooperation and Development show that in developed nations, girls started outpacing boys in educational achievement starting in the 1960s. These days, girls earn 57 percent of bachelor’s degrees, and 51.8 percent of PhDs.

While boys still have a slight edge on international standardized math tests, girls blow them away on reading tests; and, no matter the subject, girls consistently get better grades. These rifts have caused something of a crisis among educators, who wonder what is disadvantaging the world’s boys. Or, to frame the question a different way — how did girls get so good at school?

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One theory says that the school environment itself favors girls, who tend to be more organized and more diligent. According to the OECD, girls spend more time on their homework, are more likely to say they enjoy school, and more likely to show up to school on time. Girls are also less impulsive and less likely to be punished in school. This could explain why low-performing students are disproportionately boys, whose behavioral problems are holding them back.

Research from the United States shows that there’s something about girls that makes them more resilient to adverse circumstances. Put a boy into a low-income household or a low-performing school, and he’ll wither; put a girl in those same situations, and she’ll endure. Many suspect that boys may be ill-equipped, both emotionally and psychologically, to deal with challenges at young ages.

“There are a lot of studies that show boys have trouble with what we call ‘soft skills,' ” economist David Autor told me a few months ago. “They're more impulsive, they have more trouble containing themselves. It takes a lot of work help boys overcome those behavioral traits.”

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But what if some of the academic disadvantage for boys results from deeper biological differences?

A few years ago, one school district in Europe stumbled across a surprising way to narrow the gender gap: starting the school day in the afternoon.

It was a unique situation. One month, high school would be held in the mornings, while middle school would be held in the afternoon. In the next month, middle school would be held in the morning and high school would be held in the afternoon. For the entire school year, students would switch off between starting school at 7:30 a.m., or starting school at 1:30 p.m.

According to a new study from economists at the University of California at Davis, starting school in the afternoon gave a surprising boost to boys. In the months when their classes were held in the afternoon, boys got slightly better grades on their assignments and tests. It wasn’t enough to totally erase the gender gap, it did close 12 to 16 percent of the difference in grades between boys and girls.

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What caused boys to catch up to girls in the afternoon blocks? The researchers have a provocative theory. They believe that it has to do with sleep habits. Psychological studies show that girls tend to perform better than boys when sleep deprived. Girls also run on slightly different schedules than boys. Surveys find that girls are more likely to be “morning” people; they are more likely to go to bed earlier and get up earlier.

There’s been plenty of research on the salutary effects of starting school later. One classic paper from 2011 followed college students at the U.S. Air Force Academy who were randomly forced to attend early-morning classes. Those who had to get up early did worse on all their classes throughout the day.

On the basis of that and other evidence, many school districts have experimented with delaying the starting bell. To ensure that teens get enough sleep, the Centers for Disease Control and Prevention recommends that classes begin no earlier than 8:30 a.m., though a recent report found that 5 out of 6 school districts start the day before then.

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This new paper, which was recently released by the Institute for the Study of Labor and is still undergoing peer review, seems to be the first to observe that starting school later in the day helps boys more than girls. Previous studies might not have picked up on this fact because they looked at relatively minor changes in class schedules. This study is unique because students sometimes weren’t getting to school until the afternoon.

It’s hard to say, then, what practical lessons this research holds for students in America, where few school districts would change their schedule so drastically. But if sleep deprivation is the real culprit here, schools could experiment with nap rooms, or parents could be more vigilant about bedtimes. The researchers also found that the classes with the biggest gender gaps were the ones held earliest in the day, suggesting that early-morning tiredness or perhaps even tardiness might be part of the problem. In that case, schools might consider shifting classes around, scheduling STEM classes, which boys tend to perform better in, for the mornings, and humanities classes for the afternoon.

More broadly, this research should cause us to think twice about structural sexism, both in schools and in the workplace. Gender disparities these days are more likely to result from subtle factors rather than outright discrimination. Women earn less than men in part because women choose jobs and careers that are more flexible and family-friendly. But why does job flexibility have to come with a pay cut? As economist Claudia Goldin has argued, there are many occupations that are unnecessarily wedded to a 9-to-5 schedule. Our concept of a regular work day — eight hours of uninterrupted time surrounded by co-workers — puts women at a disadvantage.

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Likewise, it’s becoming clear that our concept of the modern schoolroom may inadvertently hobble boys. Maybe boys just aren’t good at sitting still for several hours listening to teachers talk. Maybe boys have more trouble keeping track of homework and staying organized. And maybe boys have a harder time dealing with the sleep deprivation that afflicts pretty much every high school student these days.

So if we want to help boys do better in school, and women to earn more money at work, maybe we should rethink some of our institutional defaults. Why do our jobs insist on inflexible hours? Why do we value competitiveness in our leaders instead of cooperativeness?