Boys tend to be better at math. That’s been the stereotype, but a new study (Kane and Mertz, 2011) published in the Notices of the American Mathematical Society provides evidence that, at all levels, it’s only because society and culture tend to support, and advance the stereotype.
… we conclude that gender equity and other sociocultural factors, not national income, school type, or religion per se, are the primary determinants of mathematics performance at all levels for both boys and girls. … It is fully consistent with socioeconomic status of the home environment being a primary determinant for success of children in school.
— Kane and Mertz, 2011: Debunking Myths about Gender and Mathematics Performance in Notices of the American Mathematical Society.
Kane and Mertz compared math achievement in a number of countries. If there were some genetic reason for different math abilities then boys should be better than girls everywhere. This is not the case. In more wealthy countries where there is more equality between the genders, the mathematics performance gap disappears.