ITA with Val. Just give him his options and let him decide. He should have no problem filling in the gaps and it would be so much better to get individual math attention (!) for a few hours this summer than to sit through next year when he wouldn't be learning anything new until three-fourths of the way through. BTW: the hesitant teacher is basing her nervousness on her experience with NT kids. This is a chance for her eyes to be opened that some kids can handle and, will in fact love, the fast-paced challenging curriculum, even though they are young and accelerated.
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She thought she could, so she did.