I have to admit I don't remember a lot of the organic chemistry textbook and AD&D Player's Handbook I inhaled when I was 9 and on Ritalin, but I apparently remembered enough of the book on phone switches that digital logic was always a cinch. But that was 23 years ago. I think even five or ten years later, I remembered quite a lot of it.
(We've talked a lot on HN about whether it's worth it to go to college. That wouldn't be a half-bad metric to use as part of that decision; do you actually recall stuff from more than three months ago in school? If not, don't spend money on college. Obviously, this is not necessary to live a good life because most people seem to manage without it.)