Boys vs. girls: What’s behind the college grad gender gap?

March 27, 2013, 2:02 PM UTC

FORTUNE — The facts are plain, if puzzling: Not only do women enter college at higher rates than men, but they’re less likely to drop out once they get there. Female grads now account for about 60% of U.S. bachelor’s degree holders.

Does that mean men are less studious or committed than women are?

Not necessarily. Instead, it seems the gender gap’s roots are partly financial: Men are less willing to take on the heavy debt loads that are increasingly required to complete a college degree. When they reach the point of owing $12,500 in school loans, men “are more likely to be discouraged” than women — and to decide it makes sense to leave school and start working full-time.

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That’s according to a new study, “Gender, Debt, and Dropping Out of College,” published in a recent issue of the journal Gender & Society. The researchers, three professors from Ohio State University and Pacific Lutheran University, analyzed data from a national longitudinal study of youth from 1997 to 2011, funded by the Bureau of Labor Statistics, that included interviews with about 9,000 men and women in their 20s.

It turns out that persistent wage gaps in the labor market play a big part in motivating women to finish school. In the short term, men who drop out face no financial penalty in their entry-level salaries. Women, on the other hand, pay a steep price right away for dropping out, since female dropouts earn entry-level pay that averages $6,500 a year lower than what their male counterparts earn.

“Female dropouts simply face worse job prospects,” the authors observe. “They are more likely to be employed in lower-paying service work, while men who drop out have more opportunities in higher-paying jobs in manufacturing, construction, and transportation.”

True, but parents of college-age kids may want to emphasize one further finding: Male dropouts’ earnings advantages are short-lived. While men who leave college before graduating “don’t face a wage penalty early on, the penalty accumulates later,” the study notes. “By middle age, men with a college degree earn $20,000 a year more, on average, than men with some college but no degree.”

An unwillingness to pile on debt when they could be making money may explain why more men quit school, but what accounts for the fact that fewer men start college in the first place? In a new book called The Rise of Women: The Growing Gender Gap in Education and What It Means for American Schools, Thomas A. DiPrete and Claudia Buchmann, sociology professors at Columbia and Ohio State, respectively, tackle that thorny question — and come up with  answers that challenge conventional wisdom.

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Boys get lower grades than girls, and report liking school less, not because girls are naturally more studious or because schools aren’t “boy-friendly” enough, they write. Rather, “our research shows that boys’ underperformance in school has more to do with society’s norms about masculinity … Boys involved in extracurricular cultural activities such as music, art, drama, and foreign languages report higher levels of school engagement and get better grades than other boys. But these activities are often denigrated as un-masculine.”

DiPrete and Buchmann believe schools need to do better in two main areas. First, “the most important predictor of boys’ achievement is the extent to which the school culture expects and rewards academic effort,” they write. “We need schools that set high expectations [and] treat each student as an individual, as opposed to a gender stereotype.”

Second, the authors write, their research shows that “boys have less understanding than girls about how their future success in college and work is directly linked to their academic effort in middle school and high school.” Making that connection clear, they argue, could go a long way toward closing the gender gap in higher education.