<p>I coach a math team where the 10th graders and below routinely take the AMC 10 on the first date and the AMC 12 on the second date. The first year they went from AHSME to AMC 10&12 was 2000. Average scores on the AMC 10 were around 20 points higher than on the 12, and it made a big difference which exam 10th graders and below chose to take - but only for that one year. Since then, which exam people choose has really not made a big differerence in scores. About half the time, they do a little better on the 12. It makes a big difference in AIME cut-offs, but the actual scores are about the same for 10th graders and below who take both exams. </p>
<p>MIT may or may not know all this about AMC exams. But it still appears on the app that they are not distinguishing btwn the two AMC exams. "AMC 12/ AMC 10" are together next to the first line, with another line below. This is just like where they have "AIME" next to the first line, with another line below. On AIME, it's clear that both lines are for AIME scores. So I took it to mean that "AMC 12/AMC 10" also refers to both lines, not one test per line. If they really cared which test a score refers to, they could certainly have designed that part of the form to specify it, but they didn't. </p>
<p>I have no official word on this at all. This is just my interpretation. But I looked at the same issue with my son this year, and another student last year, when they filled out the apps. We decided to just put the two highest numbers down for AMC 10/12 regardless of test or year. Then, the two highest AIME scores regardless of year.</p>