If a child only learns from other children or only learns from adults I would think that kid is pretty well screwed. The problem with the Lord of the Flies analogy is that there is no way to totally remove adult interaction from a child's development (even if it's a less optimal interaction say with a case worker instead of a parent or teacher), so there never is this Lord of the Flies scenario that's being discussed.

The tendency is there even if it doesn't go as far as Lord of the Flies. I work at a boys school for gifted students. They are all smart and they are usually well behaved as individuals, but if they get in an unsupervised group, things can go badly rather quickly. That is why we do our best to make sure they are never unsupervised.