<p>Curmudgeon - Anecdotal recommendation from my experience. (Wish I had stats for you but I don't). My D scored 1510 on PSATs with no prep. Then did a terrible Princeton Review course for 4 weeks once or twice a week. They told her she was capable of an 800M. Scores came back, 730V 740M for a 1470. We stopped there, on the advice of the guidance counselor who I think was just sick and tired of the SAT bootcamps and the high-pressure atmosphere of the Bay Area. </p>
<p>I to this day believe that had she followed the Xiggi program and taken them again she would have gone back up above 1500. This is because she is the top math student in her class and because of the PSATs. And as she has a robust enough ego that she would have taken them on pretty well, which to me is the key factor as ohio_mom points out, were she to have to do this over again (GOD NO!) I would strongly have recommended she take them twice. </p>
<p>It goes along with what I tell my kids about a lot of stuff - just do the best you can and then whatever happens you can live with it.</p>