Why don’t more girls grow up to become scientists and engineers? It’s not that they’re bad at math, a new study argues. It’s that they’re even better at reading.

Economists Thomas Breda of the Paris School of Economics and Clotilde Napp of the French National Center for Scientific Research came to this conclusion by analyzing survey data from 300,000 high school students in 64 countries worldwide.

“We tried to understand the reasons why we observe so much segregation between girls and boys in terms of fields of study,” Breda said.

Their study, published in the Proceedings of the National Academy of Sciences,found that among the students who were better at math than at reading, 68% were boys and 32% were girls. On the flip side, among the students who were better at reading than at math, 68% were girls and 32% were boys.

This gender gap could explain why boys are more likely than girls to take the kinds of classes that lead to careers in the so-called STEM fields — science, technology, engineering and math, the researchers reported.

“People have many different areas that they might like and many different areas that they might be good at,” said sociologist Catherine Riegle-Crum of the University of Texas at Austin, who was not involved in the study.

“When making a [career] decision, it’s about weighing all of those things,” she said. “A lot of past research either hasn’t acknowledged that, or in some cases hasn’t had the data to be able to tease those things out.”

Breda and Napp were able to find that kind of data in a survey called the Program for International Student Assessment, or PISA. Administered every three years to 15-year-olds in countries all over the world, PISA catches the students before they have to decide which subjects they want to focus on.

The PISA survey administered in 2012 was of particular interest to the economists. In addition to assessing students’ math, reading and science skills, it asked them about their intent to take advanced courses in each of those subjects in the future.

On the whole, boys had a stronger attraction to math classes than girls did. For instance, the proportion of boys who said they wanted to take more math classes instead of more reading classes was nearly eight percentage points higher than it was for girls. In addition, the proportion of boys who said they intended to “study harder” in math than in reading was almost six percentage points higher than it was for girls.

In just a few countries, including Turkey and Malaysia, the proportion of girls interested in studying math was higher than it was for boys. But in most other countries, boys had the edge over girls. The most extreme example was Switzerland, where 68% of boys and 47% of girls said they were willing to take additional math classes, Napp said.

The researchers wondered whether this difference could be linked to students’ math ability. In other words, are boys simply better at math than girls?

Sort of. On both math and reading tests, the average score for all students was slightly below 500. But on the math test, the average score for boys was about 10 points higher than for girls. Meanwhile, on the reading test, the average score for girls was about 30 points higher than for boys, the researchers said.

The researchers decided to compare each student’s math skills with his or her reading skills. Here, the gender difference was more stark. In looking across the 64 countries, they saw that 59% of boys were better at math than at reading, and that 74% of girls were better at reading than at math, Breda said.

Drawn to their strengths

The results clearly debunk the idea that girls don’t have what it takes to succeed in technical careers, Riegle-Crumb said.

“It’s not that they can’t do math,” she said. “It’s that they have some skills and some interests in fields that are even greater than that.”

That insight “is pretty impressive,” said Andrei Cimpian, a developmental psychologist from New York University, who was not involved in the study. “The more you perceive yourself to be good at ‘X’ relative to ‘Y,’ the more you’re likely to pursue ‘X .’ ”

The economists also wondered how many of the students who said they intended to study math actually went on to do so.

So they questioned about 12,000 15-year-olds from Paris who had taken the PISA survey in 2015. It turned out that about 78% of students who said they intended to pursue advanced math courses did in fact enroll in them the following year.