Final Exam (1981)

The unprecedented success of HALLOWEEN and FRIDAY THE 13TH spawned a plethora of slasher movies in the early 80s most of which were pretty ordinary, like this one.  It actually starts quite well but makes the fatal mistake of not including enough incident before killing everyone off in a rush right at the end.  In fact, it's easy to reach the conclusion that either they were working without a script (or at least a complete script) or that the film was hacked to bits in the editing room.  The reason I say that is because the killer's identity and motive remains a total mystery, which is more or less the key element in these films - the big reveal right at the end when the mask is pulled off.  Don't look on that as a spoiler, look on it as me giving you 90 minutes of your life back.