You should consider medication. I used to be against medication, but after talking with a few of my friends who have gifted children, things like ADHD are extremely common. Avoiding medication and letting them spin in the wind is not a good strategy and it destroys their self esteem. Get as small a dose as possible and then wean him off as he gets older and hopefully his prefrontal cortex will catch up and help regulate him.

Piggybacking here: also consider alternative forms of education. Montessori, Waldorf, home schooling, etc.

Many are more expensive in time and money, but you may find fairly cheap alternatives.

Worth a shot at least.