I think you MUST try it now that teacher said it won't work. See what your DS is made of. Will he rise to the challenge. Give it a couple of weeks and explain to your DS that even if he understands the math, there are things that older kids are expected to do, and he should try to do those things. But, it's more important that he learn math, and if feels like he's learning, you'll stick with it. If not, you'll find another way.
Grades at this level should not matter--unless there's some program depending on a certain grade. So, I wouldn't sweat it. Let him try with the support he needs to know that it's OK if it doesn't work out. Even if he can't do all the explanation and gets a C, if he's learning, he's learning.
This is great. I think that DS will rise to the "challenge". The challenge is not the math. It's all the other stuff. Really the only reason that he is in 5th grade math at school is because this is the highest grade in the school. (Side note, a local private school has offered to allow him to go there for 6th grade math. The timing is bad, so we aren't doing it.)
We don't care about grades at all. This is something the school doesn't understand. When the teacher remarked that she didn't know how to give him a math grade given the crazy logistics, I told her not to worry about it. We don't care if he doesn't get any grade. She didn't understand that.
