My girlfriend's daughter has been doing home schooling for her 7th grade year and will likely continue into her 8th grade year due to Covid. She has been working with a couple of online math courses and getting into the Trig, Pre/Algebra, and related levels.
At this level, a calculator starts becoming necessary/useful. I've been using HP and RPN calculators for decades (even in high school) but know that's not the waay of these modern times.
I seem to recall TI (maybe the TI 84) is basically the recommendation of choice.
If buying a teen/tween a calculator to last through the rest of their grad school years, what would be the best option?
But they didn't know that non-alphanumeric / graphing calculators can still implement sophisticated numerical methods. And in case the calculator doesn't have whatever you need, it can always be programmed.
I used these algorithms to verify huge linear algebra and calculus problem solutions. Plus, learning RPN makes calculating a pleasure and can motivate the student to understand other CS concepts. The 15C or the 42S are great choices.