I was home schooled all the way through til college - never went to any regular school. I have never regretted that, and never felt that I am missing out on any skills necessary for dealing with functional adults. Indeed I see the painful impacts and lasting damage those experiences had on some of my friends, and I am glad I never had to experience it.
Kids are cruel to each other because they do not yet know any better. They are still developing empathy and have not yet learned social skills. Kids in mixed-age environments can (and do) take their cues from older children and adults; kids who are isolated into the bizarre, historically nonexistent single-age environments found in the modern school system do not have that advantage, and accordingly tend to brutalize each other. Outside of prison there is nothing like it in adult life.
Just want to point out that adults can be just as cruel or even crueler than children with just as little empathy. I don't believe or buy the idea that it just a kid thing. We live in this myth that adults are more mature but interacting with society dispels that myth drastically quick, in my experience.
I think I see a lot more kindness as an adult, but I think this is almost exclusively due to selection effects.
I do not see that kindness at the airport or the grocery store, or most other instances that are closer to a random sampling of the US adult population.
Kids are cruel to each other because they do not yet know any better. They are still developing empathy and have not yet learned social skills. Kids in mixed-age environments can (and do) take their cues from older children and adults; kids who are isolated into the bizarre, historically nonexistent single-age environments found in the modern school system do not have that advantage, and accordingly tend to brutalize each other. Outside of prison there is nothing like it in adult life.