I live in the US and its pretty common in my area for JW kids to be home schooled as well. Especially after they turn 10-11 (after 5th grade in the US). Sometimes, I see it done well. Most of the time, the kids fall behind. At least where I live, the state requires mandatory testing and proof that they kids are doing work to stay on their grade level. I have a relative with a 15 year old who was told that if she didn't catch up in a specified period of time, she would be forced back into the public school system.
I agree that most people don't have the training to educate properly. I certainly don't. Plus, kids tend to learn better from others than from a parent (at least in my house). Its a different dynamic. Of course, there's the socialization issue that is probably the biggest advantage to attending a school.
There are cases where home schooling makes sense. But, the majority of the time, I'm not convinced that its best for the child. And yes, I know some parents who sleep until 10am with their teen aged kids and I'm fairly certain the motivation for home schooling is the lack of a schedule. I know others that home school so they are free to vacation whenever they like.
Again, my personal experience may skew my opinion. I have several family members and others that I know go down the home schooling road and it hasn't ended well.