In the Netherlands we, or at least as far as I am aware besides a few exceptions, don't really have single sex schools. I personally think that it's silly to segregate the sexes. As others have mentioned, its important to learn to interact with your peers. You may become hampered if you grow up with only boys or girls. Perhaps the quality of education improves, but in practise that is useless since you need to convey that information around, without staring at that women's boobies all the time. In co-ed you've had plenty of time doing that, and you've had plenty of opportunities to learn that it's rude to do. Extremely pleasing and fun, but rude none the less.