From what I gather from my children (13 & 15, mainstream schooled), I find there to be a huge amount of wasted time. I'm sometimes under the impression that the teachers are basically glorified child minders.
I have a friend who home-schools their children, and they're much more aware of the world around them compared to others of that age.
My argument against home-schooling was that the children are missing out on the social aspects - but thinking about it, that's just wasted time which just encourages concern over trivial matters and like you say, cliques. There's also the concern of being around those with a less than desirable influence. Of course, it's not entirely negative.
Now I'm on the fence. In hindsight, I would have at least given home-schooling consideration.