And it is not only the least educated boys who are falling behind. Research by Mr. Stoet and David Geary of the University of Missouri based on PISA tests from 2000 to 2009 concluded that on average, boys score worse than girls across the three subjects in 70 percent of the countries tested.

“What will be the implication for society 20 years down the line, given that men have a larger potential for violent action?” Mr. Stoet asked. “Shouldn’t we actually be worried about this?”

The question is what to do about it.

Part of the answer is about raw development. The O.E.C.D.’s latest report suggests that economic and social progress reduces boys’ deficits. The gaps are usually smaller in more developed countries. While the O.E.C.D. did not find a systematic relation between the gender gap and socioeconomic status in the United States, the general pattern meshes with findings that American boys from poor, single-mother families tend to do worse than girls.

And yet one thing to understand is that while social and economic development might help boys, research suggests it won’t reduce girls’ math deficits. Over all, girls outperform boys on the standardized tests by some of the widest margins in relatively poor countries, like Malaysia and Thailand, and in nations like the United Arab Emirates and Qatar that have little in the way of women’s rights. The gender gap in math at the top actually widens as living conditions improve. Girls’ scores improve, but boys’ scores improve more.

Moreover, the dismal performance of so many boys in well-developed countries like the United States suggests development alone is not enough to lift their educational prospects.

The O.E.C.D.’s suggestions to close gender gaps in education are hardly earth-shattering. Top-performing girls suffer from a lack of self-confidence in their mathematical abilities. Boys, by contrast, are much more likely to be disengaged. They play more video games. They devote less time to homework and read less for fun, especially complex and demanding books.

Parents, it suggested, could do more to encourage their daughters to enter scientific and technical fields. And they could force their sons to do their homework. Teachers could be better trained to encourage girls in math and educate boys from poorer socioeconomic backgrounds. Notably, they could stop typecasting boys as troublesome, and giving them lower grades than girls. “It is unclear how ‘punishing’ boys with lower grades or requiring them to repeat grades for misbehavior will help them,” the O.E.C.D. noted. “In fact, these sanctions may further alienate them from school.”