He Who Shall Be Unnamed said:
I don't know that there is any significant prep that is targeted for the PSAT, but having recently gone through all of this with my son, a few things I would say are:
If you get NMS, it will definitely get you money from A&M and other schools. I was unpleasantly surprised as to how little it seemed to matter elsewhere.
High achieving students, as yours seem to be, benefit from private tutoring as the test scores get pretty "steep" as you reach the top. Most kids will benefit from a group class to get them the points they need. High achieving kids don't really need what is being taught in a group class.
If your kid is stronger in math, have them take the SAT. This wasn't my son's strong point, but he is an extremely fast reader. For him, the ACT was the better test (and probably contributed to his NMS status as it is twice verbal and a single math score, I believe). Speed is extremely important for taking the ACT.
All the best.
Few schools care about NM, A&M is probably one of the most obsessed about it among the Top 100 schools. Mainly Mid/Lower ranked schools give out big scholarships to NM because they like to use it as a talking point. I believe only USC, Vanderbilt, and Tufts give out any special scholarship money out of the Top 50 for NM but I may have missed one or two. None make it the pre-qualifier for major awards like A&M does though. Apparently now A&M is going to make NM as the only way to get out of ETAM as well which makes no sense.
Most Selective schools see NM as just another award. It's nice but really it just shows you did well on a test in your Junior year of HS. My son's HS has 3 kids that made NM Semi last year that I know of who weren't even Top 25% because they just test well and are bright but they don't study or have any significant activities. It's foolish for school to put too much emphasis on it. It's definitely a nice thing to have but it's far from the end all, be all predictor of success that A&M has made it out to be over grades, rigor, EC's or anything else combined outside of class rank which is also deeply flawed as a measurement.
I do hope our school wakes up at some point in the next few years and gets rid of rolling admissions, NM obsession, and of course the Top 10% rule. All of those things hold us back.