Before you start considering treatment options, I'd strongly recommend making sure you get some objective testing done. I don't know what form of "tested by a neurobehavioral specialist" you've already gone through, but objective tests exist for attention disorders. I can personally recommend the T.O.V.A. Company's test; it's a simple reaction-time test that detects a pile of different attention disorders very accurately and objectively, without regard to any subjective evaluations of behavior. Several brilliant friends of mine run that company, and they know their stuff.

Also, congratulations on having a kid who has problems in school because they're far ahead; as problems go, that's a pretty good one to have. :)