Took the ACT in 7th Grade and got a 26; which was higher than a guy who played B-ball at my high school who took it as a senior. He went on to a pretty successful college career and had had a decent stint in the NBA/Overseas so he probably can't complain. Everybody thought I was some sort of Super-genius. I got awards and offers of scholarships and it really weirded me out and was probably the turning point in my academic career from then and through high school. I "coasted" the rest of the way. I graduated middle of the road with a B average because I didn't take it seriously enough.
Took it again my Senior year (in a situation much like Johnny's. No sleep and a night of partying) and got a 23. Which wasn't bad considering it consisted of me sweating so profusely that you'd have thought I'd gone swimming and passing out during the Math portion. I happened to wake up with the proctor proclaiming "5 minutes left". This of course resulted in a frantic dash of random marks. My Math section drove me down so bad I almost didn't get into my school of choice. I had to retake it later that year and ended up with a 29.
I buckled down in college, found a niche and a method that was good for me, and was able to graduate with my B.S. in a little under 4 years. I think the average when I entered college was 5 years so it was nice to beat the math for once. Some kids, especially athletes (and especially athletes who have some socioeconomic discrepancies in relation to their peers-be they underfunded schools, poverty, race, etc), just don't take the academic part seriously enough. That isn't a knock on their intelligence or overall ability just that they don't tend to put the focus into the scholastic part like they should.
If you want to get a degree, really want it, with all the academic support systems that are in place (and if the institution and coaches place the value in it) for athletes at most of the high D-1 schools you should have no problem getting it. Add into the less talked about side (i.e. the "friendly major" for athletes that exists at most of these schools) and you really have to screw up to not succeed. Lord knows that they still do though.
I could tell you stories about the coaches having to walk Marvin Stone to class, put him in his seat, wait out front of the building for a bit and then find out after they left he walked out the back door.