My eldest son, now a rising senior, is looking at the testing requirements of specific colleges. We are surprised that Carnegie Mellon discounts SAT subject test scores from before 11th grade:

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Carnegie Mellon requires either the SAT Test or ACT Test from every applicant. SAT Subject Test results are recommended for various programs, see the chart below for details.

We believe that college admission testing in the 9th and 10th grades adds to the anxiety of a process that students will not encounter for several years. As a result, we’re generally not in favor of any 9th or 10th grade SAT Subject Tests. While they may measure subject knowledge at the time the tests are taken, that level of knowledge degrades over time and doesn’t remain representative of the subject knowledge students bring to college freshman level courses. Should students present subject tests taken two or more years in advance of their freshman experience, we have to take the timing of the test result into consideration. The greater the amount of time prior to the freshman year, the less we can rely on the test result as a fair representation of their knowledge entering freshman level courses.
I wonder how many other colleges prefer subject tests from 11th or 12th grade. My son earned a 5 on the AP Calculus BC exam in 10th grade and took multivariable calculus this year as a junior. Next year he will take discrete math, differential equations or linear algebra. I hope CMU is not too inflexible regarding SAT subject test dates.