We live in SF Bay Area.
My D refused to go to school before finishing 3rd grade at a private school because she got bored. She was ever since home-schooled, taking online classes mainly from Stanford EPGY and John Hopkins CTY until entering UC Berkeley EECS at the age of 16. At the time she was also admitted to other universities.
She did not have a high diploma nor GED certificate. She took AP and SAT exams (not classes) at a local public high school, sometimes at The Harker School because the local school could not accommodate her.
Last summer, my D taught a CS class at UC Berkeley. The top class student was an 18 yr old girl majoring in economics who would be going to a PhD program at Columbia Univ. the following fall. She took the class “just for fun.”