I have to agree with @roethlisburger here - this is an anecdote, not a controlled (or a pseudo-controlled) experiment. My D’s PSAT improved from 1300 to 1480 in a year without any tutor or prep. Would a tutor have helped her get a higher PSAT? Maybe. Would it have helped her get a better SAT? Less likely, but maybe. Would it have made the slightest difference in her college plans, even without her scholarship? Extremely unlikely.
However, my D is also just another anecdote. There are kids who need help preparing for SAT/ACT tests, there are those who are helped by prep classes/tutors, there are those who do not need them, and there are those for whom a tutor or prep class is a bad idea.
I think that parents should have their kid take a practice test in “real conditions”, and then take a different one a couple of months later. I think that the best timing is one in the fall of sophomore year, and the other the next spring. If the school provides free PSAT 9 and PSAT 10 testing, that would be even better. No tutoring and no test prep classes in between. On average, there is a 50 point or so increase without any tutoring or prep classes, just due to the classes the kid takes and the fact that a kid has taken the test before. In my opinion, any decision about tutoring/prep classes should be made based on how the change in the score looks.