The higher somebody's GPA is, does that correlate to how quickly (or slowly) they learn the offense and defense? (ie IQ)

i don't think there's a correlation

college GPA has no direct correlation, but highschool GPA is a significant factor in IQ growth, along with WE and, i believe, to a lesser extent, playing time (and of course practice time). 

now, college GPA is of course influenced by highschool GPA, so if you ran a statistical correlation between GPA and IQ, you'd probably see something, but thats only because highschool GPA impacts both. they could have taken this on with an "intelligence" rating instead, but that has the downside of 1 more not-that-important rating (i wish it was more important though). the downside of the highschool GPA is, if you don't save it, you can only see it for true freshman and juco recruits.

I wholeheartedly believe exactly what gillispie said.