In my experience, my going to school was my family's primary link to the community. I would venture to say that my parents made more (and more lasting) friendships through my school connections than I did. (Of course, they stayed in town long after I left, so they've had more of a chance to perpetuate those relationships.)

It seems to me that the biggest difference between school and homeschool isn't about learning or development, but rather that kind of participation in the community. The benefit isn't necessarily reaped by the student in question; it might be the family or the other students who benefit. If you're a kid who wants to learn with parents who want you to learn, then you make the whole community better just by being there.

I think this point gets lost on a lot of modern American parents, who seem to think purely in terms of how their own children can benefit, often at the expense of the larger community. The fear is "My kid might have to compete for a job with some kid from India" and somehow the conclusion is "I have to compete with the other parents for the teacher's time and attention," rather than "I should join forces with other parents to make sure we all succeed."