Hardly anyone is familiar with the new SAT, since it hasn't been out a year. However, one of our kids took the previous SAT at 13, and most members of my sib group took the way old SAT back in the day between ages 9 and 11. One of my young relatives took the ACT this past winter, at age 10. I think it was made clear to all of us that some of the material might be topics in which we had no prior instruction or exposure, since the tests are designed for students leaving 11th or 12th grades. Take your best guess and move on. Whether it could be demoralizing is somewhat dependent, however, on the specific child. One of our children did not end up testing, because it would have been an unnecessarily unpleasant and anxiety-provoking experience.
For my own children, I've explained that I am deliberately having them take a test with a high ceiling compared to their current nominal grade placement, so that I can track ongoing progress, and progress toward college prep, because age/grade-appropriate measures don't give enough information on progress in their cases. When it's time to apply to college, then they'll take it again "for real." Test prep consists solely of taking the practice test in the registration materials (or you could use the same test on the CB website).
