Hi BCS
Are you worried about 'gaps?'
Can you get a copy of the 5th grade Math book and look at it to see if there is much for him to learn?

I've had both experiences - times when I've 'overprepped' and times when I've 'underprepped' - it's difficult with unusual kids.

My favorite Math of the moment is
http://www.khanacademy.org/exercisedashboard?k

Best Wishes,
Grinity

Coaching available, at SchoolSuccessSolutions.com