I might even consider talking directly with the math teacher. I know in my daughters math class (which is eighth grade) they have challenge questions that the teachers don't assign them to do. They are given the option to do them if they want. Maybe the program the teacher has also has challenge questions that she doesn't give out.
on the other hand instead of buying a book I could save you some money and just send you copies of my daughters work daily. LOL
Also have you looked in to http://www.k12.com/mnva. It is a free online school for kids across the country (I pulled the one for Minnesota up for you). My daughter is currently attending the Washington one. I love how they have daily assignments but if they chose they can take extra's. IE: if he loves math he can take 10 classes a day and progress as far as he wants. They have a full time and part time option so if he wants he can take certain classes through the online program and others he can attend normally. It also generally allows them to play sports or be part of school clubs.
