Looking for title of a movie

I don't know if the movie is from Japan, Korea or Taiwan so I am posting on General discussion
I'm looking for the title of this movie I saw a few years ago:
It's about a group of school students that decide to enter their school one night and wander there talking about their problems. At one point one of the students falls in the swiming pool that is empty, killing himself 
If anyone knows this movie, kindly tell me the title
Thank you