Any other's like this?

Are there any other Korean school violence movies like this?? I like to watch and study the problems that many kids face due to school violence, because it sort of relates to my Junior High School experience (although it was definitely nothing compared to the violence displayed in this movie).

So please recommend to me any other movies like this: that have some sort of Korean school violence in them. P.S.--I've already seen "Friend". It could be a gangster movie too like "Friend"... but I would prefer school violence movies (preferably Korean).