Lori,
Given his documented diagnoses, including his difficulties sitting for extended periods of time, your son would almost certainly qualify for accomodations on the ACT and SAT, including large block answer sheet (no bubbling!), frequent breaks, taking the test in short sessions across mulitple days, and use of a keyboard on the SAT writing section. He'd probably also get a private testing room, just because the frequent breaks and extended time would make it impractical to test him in the same room with students who didn't have the same accomodations, so any hesitancy you or he might have about making him look diferent in front of his peers shouldn't play into it. He's old enough that you should start applying now - it can take a few months to get accomodations approved, but for the SAT at least, once the accomodations are approved, the approval is good through the end of high school.
I want to point out that the only way he is guaranteed to not make the scores he wants on the SAT and ACT is if he doesn't take them. If he completely bombs the tests, well, then he needs to either figure out a way to do better the next time (you can retake the tests) or figure out another way to accomplish his goals and show what he can do. But not trying is a terrible approach, and a nasty habit to get into so young.
