Detention

Detention movie synopsis:  It's another year at Grizzly Lake High School for Riley (Shanley Caswell), a clever but cynical social outcast who is the unrequited love object of Sander (Aaron David Johnson), who is even less popular and more sexually frustrated than she is. Meanwhile, ironically named hipster Clapton (Josh Hutcherson) is head over heels for lone (Spencer Locke), a beautiful but self-absorbed cheerleader. All four are waiting out their final year of high school, but standing in their way is a slasher movie killer who has seemingly come to life. As serial killer known as Cinderhella is on the loose and preying on Grizzly Lake's student body, the principal (Dane Cook) is certain that Cinderhella is a disgruntled student and figures he can keep the prom from turning into a bloodbath by putting the likely suspects in all-day detention on the day of the big dance.

Wikipedia: Detention
Check out the trailer below!