"At some level, we were looking for it," she said. "We were surprised at how strong the correlation was."
The highest performer in math was Iceland, which also has high gender equality index. Girls in that country outscored boys by more than 14 points. In Turkey, which scored low in gender gap equality, girls performed the worst: on average, 22.6 fewer points than boys.
Not every country proved the theory, however. In Indonesia and Thailand, both of which scored low in gender equality, girls outscored boys in math.
Although the study points to at least some environmental influence on girls' math performance, Sapienza stopped short of saying societies' gender equality caused the uptick in math performance, an important distinction for a scientist.
"What we established is the correlation. It's very hard to claim that the moment we change gender quality the math and reading gaps are going to change," she said.
As a woman, she said the results made her happy.
"There's at least a hint this is driven by cultures. So it may be possibly to modify [gender gap] in some societies and that's good news for everybody," she said.