There is a lot of verifiable science behind brain chemistry in boys being more developed in areas of spacial recognition and their ability to create abstract objects mentally.  Pretty much every book I’ve ever read on pedagogy and brain science has mentioned that.  This, however, does not justify the belief that because of this, girls are worse at math.  I agree with what Riegle-Crumb says, teachers probably took what they read about this (it’s not a new finding by any means) and unconsciously materialized it.  

In my opinion, this is less of an issue as the incessant belief that boys are trouble makers and the accompanying stifling of the more tactile, wild male energy in classrooms.   There has been a long standing push to try and tame boys to be more like their female classmates (especially in areas of behavior).  It’s an interesting trend that is doing some serious damage to the collective idea of “male identity” at a very young age.  I highly recommend the book “The War Against Boys” by Christina Sommers for more information:

http://www.amazon.com/The-WAR-AGAINST-BOYS-Misguided/dp/0684849577/ref=sr_1_1?ie=UTF8&qid=1334002744&sr=8-1

I agree with Brett about unconsciously materializing the notion that men are better at math and science than women.  I thought the same way at one time.  I always loved math but, as a female, never felt as though it was a career path because growing up I always heard that boys’ brains were just better designed for math.  Finally, in high school one of my (male) teachers told me that I was one of the top math students.  That one comment inspired me to get a degree in mathematics and actuarial sciences.  I just hope there are many more teachers like mine who view each student as an individual, not some statistic in a study, and use their influence to help build confidence.