Actually, the AHSME no longer exists; it has been replaced by the AMC 8, 10, and 12 as the qualifying test for the AIME. Each test can be taken only by students in or below the corresponding grade; an 11th grader is forced to take the AMC 12, rather than the AMC 10, for example. 100 is still usually the qualifying score on the AMC 12 (though it gets lowered during "difficult years", which suggests to me that high school students are getting stupider.... a notion supported by the re-scaling of the SAT.) On the AMC 10, a qualifying score is anything in the top 1%. That is as hard as it sounds. Many intelligent students, therefore, choose to take the AMC 12 even in 9th and 10th grade.