Whelp, back in my day, nearly 3 decades ago, there was the standard SAT, for which there were your Verbal and Math sections, with an average score of around 900. Then, should you be so lucky (or stupid) to try for a prestigious university which required a little more knowledge, you were required to take what was then known as the SAT Achievement Tests.
For some strange reason, people thought I was smart, and should apply to places to which I'd never be allowed to darken their doorstep, but apply I did, and took the SAT Achievement Tests in Calculus, Physics, and English Composition. Apparently I did well enough I was rejected by exactly one school, to which I'd have never been able to afford in any event, so no matter dropping names.
Well, the SAT and SAT AT's became the SAT I and SAT II's, which then were "recentered" to an average score of 1000, because darn it, it just sounded better. Then the SAT I's became a three-subject test, as has already been mentioned.
And yeah, just for shits and giggles, I took the ACT as well, as a junior. 32 composite. Pretty much tells ya all you need to know. But no, the school I eventually attended only took the SAT, and after that debacle, the school I THEN eventually attended determined qualification based on the ASVAB and NFQT.
Bottom line--tests are not an indication of success, merely potential. If you don't apply yourself, it doesn't matter how smart you are, you'll still be a failure.
But seriously, Reb--if your son presented a logical argument and did so without it looking like a 14-year old girl's text messages, he'll do fine.