Washington ? Sixteen years after Barbie dolls declared, “Math class is tough!” girls are proving that when it comes to math they are just as tough as boys.

In the largest study of its kind, girls measured up to boys in every grade, from second through 11th. The research was released Thursday in the journal Science.

Parents and teachers persist in thinking boys are simply better at math, said Janet Hyde, the University of Wisconsin-Madison researcher who led the study. And girls who grow up believing it wind up avoiding harder math classes.

“It keeps girls and women out of a lot of careers, particularly high-prestige, lucrative careers in science and technology,” Hyde said.

That’s changing, though slowly.

Women are now earning 48 percent of undergraduate college degrees in math; they still lag far behind in physics and engineering.

But in primary and secondary school, girls have caught up, with researchers attributing that advance to increasing numbers of girls taking advanced math classes such as calculus.

Hyde and her colleagues looked at annual math tests required by the No Child Left Behind education law in 2002. Ten states provided enough statistical information to review test scores by gender, allowing researchers to compare the performances of more than 7 million children.

The researchers found no difference in the scores of boys versus girls – not even in high school. Studies 20 years ago showed girls and boys did equally well on math in elementary school, but girls fell behind in high school.

“Girls have now achieved gender parity in performance on standardized math tests,” Hyde said.