I started reviewing typical math questions in a SAT test prep book I have. My reaction is that preparation would make a VERY big difference. I think I will have to put together my own simplified list of things you have to know automatically.
However, I read in this book that when you apply to college, they get to see ALL of the scores from all of the times you took the test. They said that some colleges will average the scores and not just take the highest ones. I was thinking that I would have my son start taking the test several times to get him up to speed. The book said that this isn't the best thing to do. You're better off practicing at home and then taking the test. If the results are about 100 points (total) below what you get in practice, only then should you take the SAT a second time.
Haven't been there and haven't done that.
When I was in school, I took the PSAT and the SAT once, with absolutely no preparation.