Belle - I am so sorry that your school is not understanding.

Sending e-hugs. This teacher obviously doesn't get it. The accelerated work should not be a carrot or prize for good behavior; your child should be entitled to learn like everyone else.
If someone had other behavioral issues, unrelated to being gifted and not getting appropriate work, would they make that child show behavior before they implemented any workarounds or made adjustments?
I am sorry that I don't have any great advice for you, but I'm angry with you. And I send you e-hugs.