This very long NY Magazine piece meditates on that topic, "Why You Never Truly Leave High School": http://nymag.com/news/features/high-school-2013-1/

I can't remember if the author states any scholarly work to support the idea, but she talks about it at length. One thing that I think is well established is that kids mostly being around other kids all day is a relatively modern phenomenon. It's a long piece, but it resonated with me.