You really need someone with more knowledge and experience of the US school system, implications of transcripts, etc., than I have, but I'll start... It's a bit sad that your DS has to do so much demonstration of stuff he's (presumably) done long before, but I guess it's reasonable from school's point of view. Is he OK with it? If he's finding it extremely tedious and you're confident that he's solid through, say, the end of 7th grade, it might be worth asking for them to identify say 5 of the hardest questions per section for him to do, with him not having to do the other questions on the section provided he gets those right.
Once they've assessed where he is now, the more interesting question is what does he do next. I'm not familiar with IB at this level; the higher maths levels aimed at 16-18yos (I don't know the terminology) have a good reputation, particularly for encouraging investigation, so I guess that's hopeful. But almost certainly just going through the next years' work is not the optimal thing to do... Do you/he know what you want for him?
