I might actually suggest that the needs of the student are more closely watched and tended to by the academic support staff at a major program like Michigan than they are in high school. I'll say this - and I went to the same high school as Walker, albeit more than 25 years earlier - it was not a rigorous academic environment then, and it certainly isn't any better now. They do have a tradition of pushing their marquee athletes through, lifting them up over most hurdles, but not necessarily in a way that makes them better. Kind of like the old proverb about giving a man a fish rather than teaching him to fish.
I don't mean to suggest I have any insight into Walker's scholastic aptitude or potential - I don't - though I do know he had some personal/family challenges. I'm only saying that I doubt he ever had to worry about academic rigor in high school. That may be why he is having a hard time adapting to college (if indeed he is).