Here are my two cents:
We went through something similar with DS last spring, when he was in 2nd grade. We had been asking for math acceleration since the spring of 1st grade, and a year later (after the school tested him) we finally got it. He was placed in a 4th grade "gifted" class for math.
It did not work, for many reasons:
-The change didn't happen until the end of March, so he was essentially walking into the end of a class, and had numerous gaps.
-All the kids in the class were 2 years older. His new classmates apparently doted on him (he's so cute! he's so smart!) But this set up expectations for DS that he would instantly understand and excel at what was being taught. He didn't.
-Because he had never been in a math class (or probably any other class) where he didn't already know the material, he was highly embarrassed and freaked out.
The end result was that he was asked to leave the 4th grade class (he started goofing off a lot), and he was placed in a 3rd grade math class. This wasn't much better, but this time because he already knew all of the material, so was bored.
End result: we wound up pulling him out of school completely.
(Not just because of math, it was for a variety of reasons. But the math class experiment showed us that school was not going to work out.)
I feel that it's okay for kids to fail; it's a natural and healthy process. But in this case I think DS was almost set up to fail, since the circumstances were far from ideal. I'm still happy that we tried, since it could have worked out really well.
