We have a young woman who was home-schooled until college. She was a straight A student in college and got almost a perfect school in the physician assistant's board exam. She is also a wonderful person to be around.
We home-schooled our son for one year. He became fluent in five languages (not in one year, but later, based on initial tutoring). He is now a highly paid computer programmer.
That is the norm. I think it has something to do with children being formed from increased contact with the people who love them, their parents. Even the best intentioned professional teachers cannot possibly devote the attention and certainly not the love that children need.
Also, a group of children will descend to the lowest common denominator as far as behavior goes. If they spend most of their time with their peers, this becomes their character.
My daughter, (homeschooled since the 4th grade and about to graduate HS)was visiting a youth church service with a friend, and after about an hour the youth pastor asked her if she was a "homeschooler". He said he could tell because of her politness, her speech and actions compared to the other teenagers, that are in public school. He said he can usually spot the homeschooled teenagers.