Actually, ALL of the high school scores are sent, though it may be that a student can request that a particular score be stricken. College admissions officers say that it doesn't hurt to take an exam a few times, and that they only consider the high scores in each area. So a kid may get 800/800/800= 2400 by combining the best on three individual SAT tests, though of course that doesn't look quite as impressive as a "natural" 2400. I have also heard anecdotally that repeat testers are looked on with some suspicion, so it is better to avoid testing more than 3 times "on the record".
Young students who wish to have the scores remain on the record must request this from the college board.