This is an important post, and is not just for HA schools; I have heard of kids spending senior year trying to get their scores to an acceptable level for P5s and other D1s, after NLI is signed. Very stressful, so no matter what level your son is targeting, work on test scores earlier than senior year.
As others said, there is no reason not to take both SAT and ACT, in sophomore year, to see how you stand. Almost all schools only use your highest verbal score + your highest math score, they don't even have to be from the same sitting, and it doesn't matter how many times you take it, so an early bad score is not the end of the world.