By Jennifer Peltz, The Associated Press

For decades, girls have lagged behind boys on standardized math and science tests in the United States, perpetuating the stereotype that women aren’t as good at those subjects.

But a new analysis suggests the supposed gender gap may not be so big — and it’s disappearing in some grades and subjects.

A look at the latest scores on the National Assessment of Educational Progress, a congressionally mandated exam given every two years to a sample of students nationwide, shows girls essentially caught up to boys on fourth-grade math in 2017. That’s the first time girls have matched or outperformed boys on fourth-grade math since the test began in 1990.

Even bigger gains were seen in eighth grade, where the gender gap in math narrowed from 5 points in 2015 to 1 point in 2017. And, for the first time, girls slightly outscored boys on eighth-grade science.

“It’s not that boys lost ground, it’s just that girls gained,” said Peggy Carr, acting commissioner of the National Center for Education Statistics. “Overall, we do not see a gender gap in math or science.”

That’s not the conventional wisdom. Girls generally trail behind boys on math and science tests, and it’s widely attributed to innate ability.

But researchers have long said the gap may reflect societal stereotypes and biases, as well as differences in opportunities for girls and boys to develop math and science skills.

“The perception of a math and science gender gap is very persistent,” said Mitchell Chang, a professor of education at University of California, Los Angeles. “But these results really point to the fact that it is not due to innate differences between boys and girls, but more likely due to environmental and social factors.”

The new report shows some of those factors may be changing.

For example, girls are now just as likely as boys to take advanced math and science courses in high school. In 1990, boys were far more likely to take four years of math and three years of science, according to the Education Department’s statistics office.

Even in elementary school, girls are getting more exposure to math and science now that schools are starting STEM education — focusing on science, technology, engineering and math — earlier.

Some experts also say girls are getting better math and science teachers in elementary school. In the elementary grades, more girls are taught by female teachers, who may themselves have overcome math and science stereotypes and serve as role models for their students.

“Maybe that’s what it took, to have a generation of girls who have been taught mostly by female elementary school teachers,” said David Geary, a psychology professor at the University of Missouri who has written about gender and academic achievement. “Teachers, parents, coaches and mentors all have an influence.”

There’s still a long way to go, experts said. High school girls are still less likely than boys to take physics, computer science and engineering courses, and women remain underrepresented in science, technology, engineering and math careers.

“In spite of the advances documented in the report, we would still like to see progress moving a little faster,” said Marni Baker Stein, senior vice president of education at the National Center for Women & Information Technology.

But the progress report shows it’s possible for girls to do as well as boys in math and science.

“Girls can do anything,” Carr said. “The sky’s the limit.”