I purposely did NOT say ALL..... many are falling between the dumbed down cracks of our public education system where in many schools they don't teach advanced math, true history, or require proper English....and I think you know that.....
Those schools under seige by the underclass and its advocates have great difficulties (none of which HS will solve) but the vast majority of schools have a number of advanced placement courses as well as advanced courses in sciences, courses in languages. Most homeschool advocates wave their inability to teach such courses off with a "well they can take it from a junior college" which begs the question.
My children went to private and public schools and any failings in their educations were their faults not those of the schools. I attended public school in southern Arkansas and had an excellent preparation for college. My late wife was a teacher in inner city Chicago and it became clear that the GREATEST problem with children getting educated was their PARENT (it was rare to find parents) not the schools.