There seems to be an almost uncountable number of results (that sometimes conflict) on gender differences in math, and reading, and how they correlate with "gender equality" in a specific region.
A science blog talks about "A Biological Basis For Gender Differences In Math?" based on a paper by Stoet G, Geary DC, (2013), "Sex Differences in Mathematics and Reading Achievement Are Inversely Related: Within- and Across-Nation Assessment of 10 Years of PISA Data." PLoS ONE 8(3)
Their abstract partly reads:
"Across nations, boys scored higher than girls in mathematics, but lower than girls in reading. The sex difference in reading was three times as large as in mathematics. There was considerable variation in the extent of the sex differences between nations. There are countries without a sex difference in mathematics performance, and in some countries girls scored higher than boys. Boys scored lower in reading in all nations in all four PISA assessments (2000, 2003, 2006, 2009). Contrary to several previous studies, we found no evidence that the sex differences were related to nations’ gender equality indicators. Further, paradoxically, sex differences in mathematics were consistently and strongly inversely correlated with sex differences in reading: Countries with a smaller sex difference in mathematics had a larger sex difference in reading and vice versa. We demonstrate that this was not merely a between-nation, but also a within-nation effect. This effect is related to relative changes in these sex differences across the performance continuum: We did not find a sex difference in mathematics among the lowest performing students, but this is where the sex difference in reading was largest. In contrast, the sex difference in mathematics was largest among the higher performing students, and this is where the sex difference in reading was smallest."
One of those previous studies is Guiso L, Monte F, Sapienza P, Zingales L (2008) Culture, gender, and math. Science 320: 1164–1165. Another one (the authors do not cite), which focuses only on the US is by
Pope, Devin and Justin Sydnor. “A New Perspective on Stereotypical Gender Differences in Test Scores,” Journal of Economic Perspectives (2010), 24(2), 95-108.
In the paper “Explaining the Gender Gap in Math Test Scores: The Role of Competition,” (Niederle, Muriel and Lise Vesterlund,) Journal of Economic Perspectives, Spring 2010, Vol 24, Number 2, 129-144, we write about the former evidence:
"In countries that score highly on gender equality, Guiso, Monte, Sapienza, and Zingales (2008) find a smaller gender gap in mean math performance as well as in the tail of the distribution. In contrast to Pope and Sydnor (2010), they find a positive correlation between math and reading with women performing well
on both tasks in societies with greater gender equality."