Well, I'm not sure about middle/high school, but I don't think that elementary students should be separated.

I'm not talking about socializing as in talking about the latest gossip, but as in learning to be polite/ learning basic manners. Many children do not learn this at home. I am currently getting my certificate to teach elementary school, and I work in a school with 2nd and 3rd graders. Learning to be respectful to each other and to adults is important, and I think learning to be respectful to the opposite sex is valuable. Many activities for young children are designed not only to teach them facts but to teach them social skills they need. Many characteristics that people carry with them throughout their lifespans are developed in childhood.