PSAT doesn't count for anything in 10th grade, either. Only 11th grade counts, and only for NMSQT. But some people like to take it earlier for practice.
It also might be prudent to take the PSAT early if there's a possibility that the kid might matriculate to college early (rather than completing the typical 4 years of HS).
Since there is a lot of overlap between the two tests, some folks recommend killing two birds with one stone by prepping over the summer after sophomore year, and then taking both the PSAT and SAT in October of junior year.
The SATII MathII covers topics through pre-calculus: SAT Subject Test Math Level 2
It's best for a kid to take SATII Math2 when s/he has completed pre-calc, if that'll happen by the end of junior year. Otherwise, s/he can take it at the end of Algebra II, but should go through the College Board study guide to fill-in any gaps (e.g., trig). In any case, it's a good idea to review older material that might have gotten stale, and prep for the particular kinds of "tricks" that show up on the SAT.