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Wasn't there a study recently posted to this forum indicating that the greater male variability in mathematics already existed in kindergarten?

I don't remember this--but if it is the case, be aware that studies have also shown that parents (actually, specifically mothers) talk to and engage male toddlers more often on the subject of math than female toddlers. Male children are also given construction toys far more often than girls.

Actually, if we want to consider why boys might have an edge on girls when it comes to spatial skills, we might look to what toys we push on the two genders. There are studies showing that early exposure to simple building blocks is really important.