Actually, they don't, not always. There is a wide range of kids to be found in homeschooling, including those who are learning disabled, etc.
Thank you for your voice of reason. :-)
It is true that there are several homeschooling families with children who are learning disabled. But you are not right when you say that homeschoolers do not always outscore public-schooled children. (unless you are talking on an individual basis) Nationwide, it is a proven statistical fact that homeschooled children outscore public school children.
http://www.freerepublic.com/focus/f-news/991592/posts