Well I guess I would recommend starting with something less drastic than taking him out of school altogether. There is a lot that can be enjoyed about one's final winter and spring as the oldest in the school. Things one had been envious about as a 2nd grader like the 4th grader beach trip in the spring or getting to put on the musical... probably something like that for your DS even if it is a silly thing it is still meaningful.
If your schedule allows, you could acknowledge to him that it's not going well, and allow him to have this time between Thanksgiving and Xmas breaks as an extended break not so that he can give up on school but in acknowledgement that you can see something is wrong and he surely could use a real break. Let him focus on what he's interested in for a solid month or so. He only misses a few weeks but ends up with a really significant break. No make up work, just tell the school no about that, that he needs a break. What are they really going to do? They don't want to fail him, then he'll just be there being an even worse problem for another year!
Find a sympathetic educational type psychologist and tell them the whole story and let them know he needs a couple weeks off while you help the school find a solution, afraid he's spiraling into depression or whatever you feel like saying -- and get them to write an absence excusing letter. A outside letter lets the school off the hook as liable for his absence.
I don't think the goal can be to get the teachers to understand your point of view. Teachers are teachers because they believe that school works, that practice makes perfect, that they can make a difference by making kids do worksheets every day. R=They believe that working hard builds character and that not working hard destroys one's work ethic. Which doesn't mean you don't start with the teachers. Start with the teachers anyways, and say its just not going to work the way things are set up right now. Just go back and forth a bit in a polite way knowing you will get no where. Once you've talked to them politely for about 5 days move up a step.
Schedule your DS to see the school psychologist/counselor, just once at least. Let them know ahead that he's just not himself etc, that he's a hard worker normally and that you are really worried about him. Let him explain to them he's bored and hates school and all that. Dont' trust the counselor not to minimize his concerns etc, some counselors are put in terrible positions by their schools to just get the kids to conform.
Try to think about what would work. Tell the principal your fears and tell them what you've brainstormed to have it so your DS can still physically get into the building each day.
For example you could suggest he bring textbooks on what he's interested in and be excused from the work in class X and Y and get to sit at the back and read his books, as long as he passes the tests. Sure they'll say no initially but honestly they are able to grant that if they wanted to so act like they can. Just ask for what you think would work.
You could suggest he become a computer lab assistant instead of going to class. I don't know. Dont' hedge, pick things that you think actually would work.
Yes some of those things do send terrible messages about how one gets off easy if one checks out, how if one stops doing the work it will just magically disappear. The alternative though if forced to continue doing meaningless work, may be worse, that they really do just check out, that mental health suffers, that their trust in you as a parent suffers.
So the bottom line is do something, because then your DS sees you are listening.
So becomes a discussion of the least worrisome path. Don't be afraid of taking on the school in some unconventional way, asking for something completely nuts. Just keep stating your fears until they come up with something better.
