Im looking for a horror movie I saw many years ago and I've been looking for it on the internet for past 2 years. It was about teenagers who were stuck in the school after hours and couldn't get out. Some man, monster or something were in the school killing the students. I remember the police being outside and the student couldn't get out because of the bulletproof windows. I also remember two students being killed one was found at the bathroom on the doors burned and the other one tried to climb out the roof window and fell down the building.

Is anyone out there who might know what movie I'm talking about ? The movie is from 1994-2000 I think.

This is only a few years old, so it's likely a miss.

Detention (2010)
IMDb synopsis:
High school students are sent to afterschool detention for unexplained reasons. There, the teenagers find themselves abandoned and locked in the classroom after the teacher leaves then mysteriously disappears. Night approaches, along with a thunderstorm. The heavy rain and lightning cause a massive power failure, throwing the school into darkness. Then, ghosts begin to appear. The teens manage to break out of the classroom only to find that the old building has taken on a life of its own, keeping them trapped inside. As they struggle to escape, they learn about the death of a student back in the Seventies. Slowly, they unravel the history of this tragedy and realize that they are somehow connected to the student's macabre and untimely death. They also soon find out that they are being held responsible for this horrific event of the past and will pay for it with their lives.

Detention (2010) - IMDb