We are in the midwest and the SAT is pretty rare, mostly we do the ACT. I had my kids take it the first time when they were in ninth or 10th grade, just to see how it went and get a feel for the test. My daughter struggles a little with standardized tests, so after she took it once, she did a test prep class that helped increase her score. My son takes after me and buzzes through the tests on instinct. I did make him take it once more, but. . .
My feeling was we knew what score each kid needed to get into their school, once they hit that score, we stopped worrying.