This study, (http://www.amazon.com/Mathematics-Education-Highly-Effective-Schools/dp/0805856897) which I've got sitting right here by some happy chance, discusses that very question, and the verdict is quite clear: the schools in the study achieve success rates upwards of 98% at getting ALL their students ready for university mathematics programs. One of the schools is a girls-only school.

Boys tend to deal with abstractions without concrete materials better than girls do, but when given the opportunity to explore through the four stages of mathematical learning, girls can and do succeed just as well as boys. The fact that a large number of math teachers don't know how to teach them that way is not their fault.