I was in 4th grade, but attended 8th grade math, science, English, and history (there was a 4 grade cap until after 8th grade classes) while my homeroom, Phys. ed., and social studies were with my 4th grade age peers.
Some teachers at the school were also accredited as faculty at a nearby college, and for students who were able to take courses which weren't able to be taught, either a professor from the college would come to the school to be taught, or arrangements would be made to bus students to the college.
It wasn't uncommon for students to be awarded a college diploma along with their high school diploma at graduation and there were multiple instances of multiple majors being completed.
Not to mention I was no longer graded on attendance or "participation". What a relief. Sometimes I'd skip my last class and have lunch at my high school with my friends (I was technically dual-enrolled). They'd go back to class and I'd go goof off.
Needless to say, the following year about 2/3rds of them selected community college.