You don’t need a prep course to do well in the SAT. I did quite well with no work at all beyond school work, and I know kids today where it’s the same.
As others have indicated, you can just buy a prep book if you want and be done with it. The prep courses are just separating parents from their money.
Yes. Just take lots of exams under strict time constraints, preferably under more adverse conditions (a public place with distracting chatter, a room that’s too cold, etc.).
And don’t bother with fake exams written by book publishers. They just aren’t authentic.
As others have indicated, you can just buy a prep book if you want and be done with it. The prep courses are just separating parents from their money.