I went to an all-boys high school. Before that, I went to a regular run-of-the-mill public high school.
I gotta tell you, the all-boys school was probably the closest thing to a school utopia I'd ever seen. There were no cliques, no social segregation, no bullies, no exclusion, and few serious rivalries (beyond friendly sports and house competitions).
The popularity ladder was nonexistent. The sports jocks hung out with the math geeks. The math geeks hung out with the musos, the musos hung out with the computer nerds. Everyone meshed with everyone else - and everyone considered everyone else on equal terms.
The fact that there were no girls wasn't too bad, you quickly grew accustomed to it. Since there were no students of the opposite sex, there was really nobody to impress. There were no idiotic stunts performed, no pointless rebellion, no stupid acts to try and impress others.
The fact that it was a selective school (you had to pass an entrance exam to get in) might have had something to do with it as well. But we were still a government-funded public school, and I think the experience would have been much different if it was a co-ed school. I spent four years of my high-school life there, and I can honestly say I very much enjoyed it. I have very few bad memories from those years, and many good ones.