I appear to be in the minority here. Can I ask why people are so anti them?
For me it's the fact that by seperating the sexes you are creating some sort of mystery about the opposite sex. By going to the same school you are taking that away and therefore when the hormones kick in they have been around the opposite sex long enough to know there isn't actually any mystery.
If a child is going to get distracted by someone of the opposite sex they are going to find someone to get distracted by even if they don't go to the same school.