Statistics were in fact quoted last night for a school (I don't remember which one.) Without knowing the sample size and how they were collected, at face value they seemed pretty impressive. I think it was 100% graduation vs. 68%, and 86% going to college vs. 31%, for a specific charter school (girls only) vs. the public school.

I think it's a good idea with the usual caveats on making sure the resources are allocated fairly between boys' and girls' schools. At the end of the day, it should be up to the parents (and perhaps the student him/herself) if single-gender classes are right for them.