One of the issues that frequently comes up in discussions with parents who call or attend my presentations at CTD is home schooling. I "partially home schooled" one of my gifted students when he was in sixth grade and wanted to learn plane geometry. His school recognized that his needs in math were not being met at school, so he was permitted to leave during the school day to come to my home for math. (This was about five years ago, so I don't remember whether we did this once or twice a week, but it was never more than twice a week.) He was able to get his other subjects at school and maintain a full complement of after-school activities. Of course, when he got to the high school, they made him jump through hoops in order NOT to have to repeat the course, but that's another story. The bottom line was that he did not take geometry in high school.
In the elementary grades, teachers and schools tend to be more willing to acknowledge that a student's needs are beyond them, and to let parents take their child out of school for part of the weekly schedule, either to homeschool the student themselves or to hire someone (like me) to mentor their child in mathematics. There is typically less flexibility on the part of the schools in grades 6-12, where many schools take the position that offering algebra in grade 8 (or, rarely, in grade 7) solves the "problem." In my opinion, it usually does NOT.
For a fuller explanation of partial home schooling, check out this article by Deborah Ruf:
I think this is a viable option for children who are particularly gifted in one subject matter area. The children can get what they need in math, for example, from someone with the expertise to provide appropriately challenging content without sacrificing all the social advantages to staying in school for most of the day. The cons include extra driving and the expense, which usually must be handled by the parents.