As I was saying, there's nothing quite like Prison School in my opinion, but shows with similar themes/styles of comedy would be things like:
Golden Boy (English Dub preferably)
Excel Saga (English Dub preferably)
Plastic Neesan
Cromartie High School
Daily Lives of High School Boys
Yondemasu yo, Azazel-san.
Oruchuban Ebichu
Ishida to Asakura