I'm relatively new to coaching (6-8 months) and don't want to charge much but obviously would like something for the time/effort I put into it.
How much you charge depends on what your goals are for the revenue you take in and how much you value what you are doing. Are you just doing this primarily as a charity, or to cover-expenses only, or just as a hobby or do you actually want to make some tangible income off it?
I've coached adult athletes online since 2019. I started charging $125/month for online-based private coaching. Then in 2021, I increased my standard rate to $200/month. This allowed me to coach full-time with a roster of 20-30 adult athletes.
I think you are talking about high school students specifically, so you'd probably be looking for their parents to pay for them in this case. I have a friend who coaches a high school winter training session and makes like $2000 a month coaching 15 or so kids in person (not sure the exact details).