> I can not conceive of a worse way to teach a kid how to behave in Adult social settings than to throw them into a group of other kids who have just as little experience as they do and then expect the group to "figure it out".

You are aware of teachers, yes?

> Probably because well run homeschooling groups tend to have high parental involvement

Everything I've read shows that putting absolutely all else aside, parental involvement is key to a child's success. So perhaps the reason your by the numbers evidence shows home schooling to be better is simply because it's a self-selecting group of involved parents.

Teachers at a school do not fill the same role that homeschooling parents do in theses situations.