I was homeschooled/self-taught since the 2nd grade until about high school when I started attending community college full-time. At that point I was about "even" with my best friend, who is also considered very intelligent. I was then able to pick which semester-long classes to take. For example, I was taking third year calculus my sophomore year, a full year before he was able to take Calc 1. And this was no discrepancy due to ability. (for those curious I applied to colleges at the 'regular' time and am now attending a 4-year institution without transferring any of my credits).
The fact of the matter is that the American public school system wasn't developed with education in mind, and now functions more as crowd control than as an educational institution.