One reason some families are willing to pay $35000/year to send their kids to the high end private schools, either boarding schools or elite day schools, e.g., https://en.wikipedia.org/wiki/Dalton_School.
Many public schools allow students to partially enroll in a community college and take classes there. At the very least, if you take a modest amount of initiative, you can negotiate a way to allow for a mild deviation form the standard curriculum.
Sadly that's the low end of private high schools. Many are over 50K and most are over 40K in silicon valley.
Not surprised it's way higher now.