For something completely different that thickens problem solving skills, you could look at Beast Academy by Art of Problem Solving. http://www.artofproblemsolving.com/Store/beastacademy.php?
If the style clicks for him (comic book content presentation with puzzle type problems,) it might be pretty motivational.

Alternatively if there are computers in the classroom that he could use, there are a ton of options in that direction.