It uses standardized test scores. I quote findings below. Remarks inside parentheses are mine.
"The third column in table S1, reports the estimated male/female variance ratios with standard errors in parentheses. In all but five countries (There are 41 countries) we can reject the hypothesis that the variance ratio is equal to one at 5% level. In all the countries where this hypothesis is rejected, the variance ratios are larger than one indicating that the male variance in reading is higher than the female variance."
In other words, male variance > female variance with 95% significance level in 36 countries, and no statistically significant difference in 5 countries. There is no countries where female variance > male variance with statistical significance.
There are various interpretations of this result. The usual interpretation is that there is a sex difference in variability. Another interpretation is that since variability difference is not universal (in 5 countries it is not statistically significant), variability difference is cultural. The later interpretation is argued in PNAS paper cited below.