Gifted Issues Discussion homepage Forums Learning Environments at a loss

Pdxgft, this is a recurring theme amongst many PG kids. So, your best bet is taking his IQ test report and the narrative comments made by you kid's tester to the school Psychologist or Counselor and having the same conversation that you are having here. The fact that he is PG, knows the math, the repetition and boredom have made him develop School Anxiety and that he is depressed about his coming school year needs to be recorded if you plan to stay on in this school.
But, until the matter is resolved to your son's satisfaction, some things can be done from your side. Increase the math enrichment at after school time: either join a math circle, join a math competition group (AMC, MOEMs etc) or enroll him in an online AOPS course/self study AOPS. This will help him be stimulated by math instead of giving up on learning more math because he is worried that he would get even more out-of-sync with his current peers.
Ask the school counselor if the kid can move to the higher math group based on classroom observation by the teacher (many private schools value teacher's observation more than test results). That could be very useful in your case.
Have your son participate in some math contests and Talent Search exams - for the main reason that it teaches the child how to handle timed tests and how to organize his work under time pressure.
In our case, we ended up changing schools because the fight to get the desired acceleration was sucking up too much mental energy from both the child and the parent. That might also be a worthy choice to evaluate at this point.

Good luck.