Out of interest, would noncompliant/disengaged behaviour be a red-flag for a disorder of some kind? He goes to after-care between school ending and us picking him up at 16:30, and does most of his homework there, and recently they've commented that he is whizzing through all of it and is doing so well. BUT when we do have some left to do at home he can kick up a royal stink about it. "Studying" for tests (ie, learning how to answer the questions rather than learning the actual material), has been the worst experience for me with him yet - it is so frustrating because I know he knows it and could do it easily but he just fights doing any of it every step of the way... For now I've told him we are taking a break. The spelling tests are still asking him to spell words like tree, fall, call, etc, so I don't even bother revising those with him because he gives me a look and then we end up doing words like gymnastics or brought... It just seems like a waste... and quite... degrading to ask him to spell "call" after that...?
Sounds like you've already got an explanation that doesn't involve a disorder. Your last sentence says it all. I would add that, given that his work ethic is different at after-care than at home, he's still the same boy in both, so that contraindicates a disorder. Rather, he values his time at home as his personal time, whereas the after-care time is not, so he might as well get some homework done.
After doing some more reading today, both hubby and I are wondering if dysgraphia may not be a strong candidate for some of the problems he's having. He forms a few letters very oddly, and punctuation isn't great while spacing is often awful. This is all far more pronounced at school than it is at home. When he's writing of his own accord, and about a topic he chose and is interested in, there's quite a big difference in the writing samples.
Again, this behavior is contraindicative of a disorder. He's still the same boy whether he's writing for school or writing for fun. I'm no professional, but my understanding of dysgraphia is that, absent masochistic tendencies, "writing of his own accord" is not a thing, for the same reason that children don't frequently run their writing hands through a pasta press.