<p>i think it has a lot to do with how good of a student you are (most CC people likely get high marks in that area) how self-motivated you are, and if you can do OK on tests.
I self studied an AP micro 5, easiest test ever lol. I think for the right kind of people (some just are good enough students, pretty committed, end up getting loads of 5's, while others rarely get 5's) can self study themselves to tons of 4's or 5's.</p>