Prison has a lot negative connotations attached to it. Prison is a place where the wrongdoers of society go as punishment for their crimes against humanity. From killing to theft, prison is designed as a correctional institute. Whether or not that actually happens is a topic for another day, but at the minimum prison, as people know it, is a place that you do not want to end up.
Prison School is the same. “School” in the title should not fool anyone; this prison is more like a torture chamber than a place of reform. That sounds absurd – and it is – but that is exactly what the anime thrives on: absurdity. Of course there are other undeniable motifs throughout the show but those, too, always have their absurdity cranked up to eleven and then some.
Speaking about myself, I have never been to prison (and I plan to keep it that way forever). Furthermore neither my immediate nor extended family has ever had anyone in prison. My father did go to his local jail once when he was in his late teens, though. He and his friends had gotten into a scuffle with others, landing them all in a jail cell for the night. “But I wasn’t scared of the place,” my father always says when recounting this small tale, “I was scared of what my dad was going to do me when he found out.” And that surmises Prison School pretty well: it is not the prison, but the people, that should be feared.