“Study hall” = detention for infraction
The “infraction” of being politically incorrect.
Back in my day, detention was during lunch or after school and was for an infraction. Study hall was for when we had a class period with no actual class to go to (we were required to be in school, on school grounds during this time, so we had to go somewhere). In my case, I had dropped a class, didn't need to take another class to make up for it, but had to be on campus and accounted for during the class period. So, I went to study hall.