From what I've heard, different med schools do different things. I read somewhere on SDN that Tufts takes your highest score in each section, but I could be wrong. And I've definitely heard of some that average multiple MCATs, while others take your most recent score. I'd do some searches on SDN and see if anyone has compiled a list of which schools do which. If not, I guess you'll have to hit the web sites of the schools you're interested in to find out, call them, or double check the MSAR (don't know if it says it in there or not).