I have to disagree that MOOC's are actually a good measure of college readiness in and of themselves. They may be a reasonably good measure of readiness within a subject for advanced material in that subject-- but they are NOT the kind of synchronous participatory and output-oriented environment that a B&M course is. They have their own challenges, but they aren't directly comparable to the on-campus or hybrid class. (Yes, I've run through a couple of these and so has my DD-- just for fun.) I'd say that the MOOC is a lot more like one of two things--
graduate seminar classes, where most of it is about exploratory learning
community education classes-- basically no prerequisites, but they aren't really college-level in either critical thinking or in background knowledge expectations, and definitely not in terms of written output demand.
They also don't include the level of graded work that campus classes do-- which is, I suspect, the reason why you (or your DS) may be overlooking the written output demands of conventional college courses.
My DD consistently underestimates it, too-- it's not just you. We know (because of our background) but she doesn't.
If he's open to it, I might have him try an EPGY class or something else using a distance model through one of the big talent search centers such as CTY. He'd meet other HG+/PG kids that way, which is HUGE, and he'd also probably find the challenge a lot closer to what he needs.
