Actually, the school can ask if he is medicated. That's typically part of the health record collected by the school nurse, for good medical reasons (in an emergency, it's important to know what medications a child may be on, in case of interactions, side effects, toxicity, etc.). But you can certainly say you'll include that kind of information on the standard medical form, when you send it in to the nurse, rather than discussing his health record with the principal.
It's true that medication cannot be used in determining disability status. Nor can the school force you to medicate him, nor withhold accommodations because you choose to medicate or not medicate him. ADHD also definitely cannot be used per se as a factor in the gifted eligibility process, as that would be clear discrimination on the basis of a disability.
