I had a pretty rough transition to college (for different reasons than people typically do), but I didn't get my diagnosis until halfway through my freshman year. It should definitely help that your son is already diagnosed. And even with the rough start, I'm a semester away from having a 3.0, and I have an internship lined up for the summer.
So keep two things in mind: you already have the best tools for helping him (the diagnosis and awareness), and even if things do turn sour, in no way does it mean success is gone for good.
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I'm never gonna dance again, Aspie feet have got no rhythm.