Best school I went to divided classes between academic and social --- social classes (gym (physical education), social studies/history, homeroom, &c.) were attended at one's age/grade level --- for academic classes (English, science, math) one attended at one's grade level up to 4 grades ahead, until 8th grade when the cap was removed.

For students who finished high school courses, some teachers were certified by the local college to teach college level courses (all teachers at this school had at least a Master's degree) and there were arrangements to students to the college, or bring faculty from the college to the school, depending on the number of students taking a given class.

Many students when graduating from high school were simultaneously awarded college degrees.