On the internet, I read that nearly 8 million people play high school sports. This is reduced to 480,000 at the college level which is about 16.7% of the high school numbers, but only 2% of this college number go pro.
If you want a breakdown of how many college athletes graduate, here are the numbers I found. Of all Division I athletes, 86% graduate. This drops to 71% for Division II. The highest percentage of college athletes to graduate come from Division III schools, but it is only 1% higher than Division I. I read this as Division II athletes either cannot handle the rigors of college or they think they are going pro anyway so why pay Division I costs. I have no statistics to back this up, however.
It is still impressive that the number of graduates is as high as it is knowing how much time it takes to play any type of college sport and still maintain your GPA.