[viola11]

Reading the supplementary material (since that isn't paywalled) I not that these are not IQ tests, but results from mathematics and reading comprehension tests.

I also found this little thing that implies that the score distributions aren't symmetric (I think):

"There is no clear pattern in the male to female ratios at the bottom 5% of the math distribution. This ratio is different from one in only 15 countries but in some countries it is larger than one and in others smaller. On the other hand, at the top 5% the ratio of boys to girls is larger than one in 35 countries with the highest estimated ratio in Korea (2.55). In these 35 countries, boys are clearly over-represented at the top end of the math distribution. The quantile differences at 5th and 95th quantiles confirm the same finding, with no clear pattern at the 5th quantile but positive and significant differences in all but five countries at the 95th quantile. "

Doing a quick test, I took some random normal numbers with variance ratio 1.4, and found that the variance ratio is not very sensitive to if I calculate it using the full sample, the bottom half or the top half. In other words, for a normal distribution the reported ratios for the 5th and 95th quantile should be the same within the errors, but this is never the case for mathematics so the scores simply aren't normal.