Yes, I've certianly lives through this with my DS, now 13! It was part what motivated me to afterschool, change schools, and come to believe that a gradeskip was needed. There was much gnashing of teeth and tears as we went.
I believe that we have beaten this syndrome - last night we had tears at bedtime because he wanted to stay up and program his calculator to solve for the Pathagorian Theorem. Now that is what a gifted kids is 'supposed to be like' in my book! So it is possible.
My belief is that if a child is forced into underachievement, and spends many hours a day way way below his readiness to learn level, then the width of his readiness to learn level shrinks, or even temporarily dissapears altogether. Your job is to keep him in environments, at home or at school, where he is given tasks that are as close as you can guess to his actual readiness level, and then sit tight while he rages his way out of the Goldilocks problem.
Since the teacher seems ready to help, ask her to keep giving him tests until she finds an area where he doesn't already know everything. She may need to bump him up 2 or 3 grade levels. I wouldn't keep giving him 'multilayered' math challenges, because he doesn't have confidence in the learning process yet. I would just keep giving him work that 'normal' older kids can do that he happens not to know yet.
It might be better to use a Aleks.com or NWEA's MAP to have an interactive assesment - otherwise this could become burdensome to all involved. You can get a free trial for Aleks this evening and just see where he is.
Best Wishes,
Grinity
