I know many kids in Kumon and it seems that they are put in by parents wanting to improve their skills or give them an academic advantage. These kids seem to be pushed a little hard to be at the top of the class. I have been asked by parents where we have our daughter tutored, they assume she is, but she is not. I have never thought of it for gifted kids, it would offer them higher levels of work, but I think it is designed as an adjunct for regular class. Maybe they are trying to capitalize on the needs of the gifted group which could be interesting. I think it is expensive.
