Was the move because of military? I just ask because in the past few years, they have started the School Liaison program. That can be an additional advocating tool if available.
Ask if the school would consider letting him spend a week in a 1st grade classroom and see if that sparks his attention and spirit. Our DS's experience sounds similar. Enriched preschool (they actually allowed him to attend their private Kinder program because he was so much happier with older kids). Then public Kindergarten where he was just way ahead from the start. He was pretty flexible with the classroom that Kinder year because he understood that he got to go to Kinder a year early and it was only half day anyway. 1st grade he was miserable from the start and shut down.
We had him privately tested (WISC-IV) so we could get some idea of what to do. We already had it in our heads that acceleration/ grade skip might the easiest way to handle his frustrations. The private evaluation also agreed that he was a candidate for a grade skip. At first the principal said no, but I also appealed to the school psychologist and after speaking with DS (he was positive about the idea of skipping - also very well-behaved and tall for his age). They gave him benchmark tests (which he passed) and VOILA. End of October he went from 1st to a 2nd grade classroom. He was still ahead in math and reading, but he had work to do in writing that kept him challenged.
I'm not sure how common/accepted acceleration is in the public schools (I'm sure it depends on the school district). But if you feel like your son might be a candidate, a private evaluation might help you advocate better. In our case, it just hadn't been done before and people needed to "have their minds opened" to the possibility. In addition, the right teacher makes a world of a difference.
