I'd be cautious about assuming he's really a full-on whole language reader. He may just be resistant for other reasons (finds the question beneath him, thinks it's a trick question, hasn't consciously thought about it in ages, dislikes the teacher). I thought my self-taught DD was a whole-language reader, but when I really paid attention it became clear that she couldn't possibly be, although she did use quick whole-word recognition as part of her arsenal. Can he, for instance, sound out things like unknown dinosaur names?
FWIW, my DS4 can't spell nearly as well as he can read. I THINK this is common in early readers? He hasn't been much of a "write to learn to read" kid. DD did more of that.
