Need info on Math impairments

I have looked at the books for older kids. They look good for older kids who don't need a lot of practice and catch on quickly. I think my husband would have loved them. I haven't been able to look over copies of the Life of Fred for younger kids yet. So far Right Start math is going pretty well, lots of hands on...maybe a little more retention of facts but I am not sure. We are up to about lesson 24. I started from the very beginning on that because I realized he didn't know how many fingers he had on a hand...he couldn't remember and he couldn't visualize it. He does know that now, and two hands, and most facts that add to 10. But, I would like to know more about the brain and how it works for kids like him. We have an appointment to do evaluation, but they moved the first appointment from end of November to 3rd week in December. The actual eval would be after Jan 1, when it sounds like my husband is going to be 1/2 time and lose insurance. Well, maybe I can get some book suggestions anyhow from that 1st meeting.