Hi T.,
First be sure your son's problem is simply being unchallenged and not some undiagnosed learning disability. Did the problem only present this year? Is some social issue causing the problem? Is this his way of getting attention from you while your attention is split with younger siblings? Negative attention is still attention. I would suggest you have your son CORE evaluated in order to have concrete information regarding his abilities or disabilities.
If your son is as gifted as you say he is than I would suggest meeting with his guidance counselor to discuss finding a more challenging curriculum that better meets his academic needs and helps him to meet his potential.
Meanwhile, take this as an opportunity to teach discipline, respect and work ethic; traits even a genius would benefit from.
You say you have used taking away things, etc. Have you tried using his sense of reason? Explain to him you are trying to help find a better fit for him, but meanwhile, he needs to prove he is worthy of peoples' effort by doing his part.
Explain that there are plenty of menial jobs that YOU do which are also boring, not challenging, etc. (clean the toilet, fold laundry etc.) Also explain to him that his teacher is his boss. He/she assigned this work and it is
disrespectful not to do it.
There are many different types of intelligence, musical, artistic, physical, mathematical, social, etc. All children have strengths and weakness. Your son is no exception to this. As a parent it is your job to help him find his talent and to foster growth in that area. It is also your job to teach him discipline, respect for others and the ability to delay gratification. See this as an opportunity to teach these valuable lessons.
Think very carefully before moving your son ahead a grade. Your son's social adjustment is just as important as his academic progress. Unless your son is truly a prodigy, I would try to keep him with his classmates while working with the teacher (or outside programs) to find opportunities for challenge.
Bottom line, if he is as gifted as you say, he will be done with the work in no time and he will then have much more free time to do with what he wants. He should be able to understand this simple cause and affect.
You are the mom, sometimes it is ok to say "because I said so that's why!" Best Wishes.
J. L.