Polarbear has tons of good advice. I'll just add a bit. From what you've said, this school regularly pretests for changes placement accordingly. This sounds pretty reasonable. Will your child be able to move up again for the next unit? If so, you will have to make a good case for why your kiddo needs to move up now. Are the things missed on the pretest things that can quickly be explained to your kiddo, or just a matter of terminology he forgot or simple mistakes? If the majority of the unit will be material he already knows, it doesn't seem fair to make him sit through the whole thIng again, not learning anything new.
Also, don't forget to write down a summary of what was said at the meeting and email everyone with a summary of what you believe were the next steps.
I once brought "peace donuts" to a meeting after a heated discussion with staff, apologizing for starting off on the wrong foot and asking of we could start over. That helped. In your situation, I would start by apologizing to the principal for catching him unawares and without a scheduled meeting.
I very much agree that you need to discuss appropriate classroom behavior with your kiddo. It does seem that he is trying to show what he knows, but he needs to learn to do this by the class rules.
Also agree that most teachers will respond only to tests they are familiar with, and will ignore IQ tests. You may have better luck with the school psychologist if you want someone to get those other scores, but truthfully they are more familiar with the other end of the spectrum. If there is a procedure in the school or the district for acceleration, get to know it. Good luck!
