Everyone I know uses some version. You can get the Princeton Review on-line (if you have a self-motivated student), or attend the courses you mentioned. High schools sometimes offer them, as well. Because my son had high PSAT scores, we choose a private tutoring package. Doing something almost feels like a requirement to stay competitive.
The SAT is changing, though, with the intention of not allowing prep courses and tutors to create an advantage. You weren't supposed to be able to "study" for it. But, of course, people figured out how to do that just that: study for it. And, thus, we have the prep class system.
My son didn't mind his classes but, of course, they were 100% tailored to him, since we had a tutoring package. Maybe that was worth the cost alone, lol: not a single complaint! Come to think of it, has that EVER happened before with my son???
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).