Ah, and for math...
My son did Dreambox, which is on the fluffy side but very game-like and nicely animated. It is supposed to cover K-3rd grade (so a bit below what the WIAT thinks your son is at), although my son hasn't realized he is done with the program (but frankly watching him arrange virtual manipulative for multiple factors of a number today completely at random until he got a match makes me doubt some of those evaluations) because he hasn't explored all the parts of the game world yet.
The drawbacks: it is designed as an afterschool/homework activity, and provides very little in-game explanations, so you will have to teach the concepts as he progresses in the game (and probably handle drilling on tables separately). But the built in assessments and the progression seem like a good guide to what needs to be taught.
Now we are starting with aleks.com, which has been recommended (with some caveats) on this forum. It starts at the third grade, has more instructions, and is not much like a game. Still waiting to see how it goes. My son likes the challenge but clearly misses the much more fun (and polished) interface in Dreambox.
