The Amazing Rise Of High School Math

THE AMAZING RISE OF HIGH SCHOOL MATH....Over at EPI, Joydeep Roy reports that high school girls are now taking as many math classes as high school boys. Plus there's this:

In another interesting development, the study found that girls are now slightly more likely than boys to take advanced math courses. In 1982, fewer than 10% of girls had completed pre-calculus or calculus, compared to about 12% of boys. By 2004, 34% of girls were completing pre-calculus or calculus, compared to 32% of boys.

That's really pretty amazing, isn't it? I mean, forget the gender gap thing for the moment. I'd guess that in the 50s, roughly 0% of high school students took pre-calculus or calculus classes. Today it's about a third. What accounts for this?