Why do girls on average lead boys for all their years in the classroom, only to fall behind in the workplace? Do girls grow up and lose their edge, while boys mature and gain theirs?

Ten years ago, no one would have thought to ask. The assumption that boys dominated at school as well as at work, while girls were silenced or ignored, seemed beyond dispute. But in her new book, “The Sexual Paradox,” a ringing salvo in the sex-difference wars, Susan Pinker stacks up the evidence of boys’ classroom woes and girls’ triumphs. “In the United States, boys are three times as likely to be placed in special education classes, twice as likely to repeat a grade and a third more likely to drop out of high school,” she writes. Tests of 15-year-olds in 30 European countries show girls far outstripping boys in reading and writing and holding their own in math. Boys are overrepresented in the top 1 percent of math achievers, but there are also more of them at the bottom. A 2006 economics study showed universities practicing affirmative action for men so that superior female applicants wouldn’t swamp them. “If you were to predict the future on the basis of school achievement alone,” Pinker writes, “the world would be a matriarchy.”

And yet, of course, it is not. Once they move from school to work, men on average earn more money and run more shows. They particularly dominate in national government, the corporate boardroom and the science laboratory. Meanwhile, women are more likely to leave the labor force and to end up with lower pay and less authority if they come back.

Pinker, a psychologist and a columnist at The Globe and Mail in Canada, is careful to remind her readers that statistics say nothing about the choices women and men make individually. Nor does she entirely discount the effect of sex discrimination or culture in shaping women’s choices. But she thinks these forces play only a bit part. To support this, Pinker quotes a female Ivy League law professor: “I am very skeptical of the notion that society discourages talented women from becoming scientists,” the professor writes. “My experience, at least from the educational phase of my life, is that the very opposite is true.” If women aren’t racing to the upper echelons of science, government and the corporate world despite decades of efforts to woo them, Pinker argues, then it must be because they are wired to resist the demands at the top of those fields.