My daughter goes to a mixed school, and she has many good friends who are male. I think it teaches teenagers how to have friendships with the opposite sex, rather than being terrified and feeling like they are a different species. I know I went to a mixed school, but it wasn't encouraged to go near boys and as a result I never knew how to talk to them. My daughter has much easier friendships with boys and behaves with them the same way as she does with her female friends and I think this will stand her in good stead as she gets older and starts to form relationships.