I'm against it generally. Unless a professional teacher is hired then you wont be teaching your children to the standard they will receive at a proper school. Plus it's incredibly hard to keep the structure of a school day at home where kids get bored and want to watch TV or play in their bedroom, but at school those things aren't options!
And then there's the whole isolation thing. They will miss out on forming social relationships and their skills and confidence growing in that area. If they decided to go to school at a later date, or to get a job etc they might feel very shy and like they don't fit in.
I guess it depends if someone is struggling in school and why, but for the most part I think that those things can be addressed while keeping a pupil in school.