There are differences amongst the highest performers, which are consistent. Believe me, it bugs me more than anyone because I was that girl--the one in all those high math classes--who couldn't believe how nonchalantly and confidently the boys took the tests. I'm sure their confidence (aloofness? unemotionality as teens? I don't know) affected their scores positively, and my insecurity, my scores negatively. I hate that it's a trend, because I'd like to think it's just my insecurity. But if you look it up, the top 5% or 2%, you will see that it is very consistently that the boys outscore the girls, and that differences between LA and math are greater, the further right you go on the bell curve.
From the OECD paper I linked earlier (which unfortunately you now have to google for, since their server uses temporary access tokens)
In four out of the six best-performing countries and
economies overall, there is little or no gender difference in mathematics performance. Among these, in the partner country and economies Chinese Taipei; Shanghai, China and Singapore, at least 10% of girls attain proficiency Level 6 in mathematics; in no OECD country, except Switzerland, do even 10% of boys reach this level.
Granted, with only 4 out of 65 countries represented here, and all of a similar culture, that does beg the question of whether there isn't some cultural phenomenon in play here that is pushing girls further.