I wish I had better advice on how to get your son through this.
I don't think I'd advise the method I used of dealing with a teacher who refused to give my son work at his level: after months of discussion, I finally just sent appropriate work in with him, and told him to do that instead during the time the class was working in that subject area, and to tell the teacher that he was working on it on my orders, and that she should discuss the situation with me if she had a problem with it. This was at a private K, and I sent in "Mrs. Frisby and the Rats of NIMH" for him to read during reading time instead of "The Bob Books". It did finally wake the teacher up to the fact that he could actually read already, which we had been telling her since the first day of school, but it didn't earn us any brownie points. It did get him differentiated work in reading.
We've homeschooled since first grade, though, for a number of reasons, one of which was that the public school wanted to make my son do all of the age-grade-level work before they would let him have work at his own level.
As a young adult, I sat through classes and completed assignments over material that I had mastered years before, but I was working for a personal goal that was extremely important to me, and these classes were required prerequisites. I'd have stood on my head and sung "Rigoletto" if that was what was required for me to get what I wanted. Having that strong incentive certainly made it a lot easier to deal with classes that would have been torture. So the only real suggestion I have to help your son get through this is bribery. If you are confident that the situation really will change, offer some really great reward that he wants and wouldn't otherwise be able to have if he complies faithfully for the next few weeks until you are able to get it sorted out. I'd offer smaller daily rewards, as well. I wouldn't ordinarily recommend this, but this is an extraordinary situation. You can look at this as him having a job he hates that he is only doing for a paycheck. People do things they love for the intrinsic reward, but you have to offer them some additional incentive to do things they hate.
