Corrected entry: Barring Joe Flood (Mr Dumpkin), Oscar James (the football coach), Mimi Wedell (Miss Mumsley) and Cullen Chambers (Charles) none of the other actors in Student Bodies (most notably the lead actress Kristen Ritter) acted in another film.
Corrected entry: When all the teachers are gathered in a room and the killer calls them, he taunts them about his crimes before saying "click" and then hanging up. However, this is impossible as both killers in the film (Principal Peters and Miss Mumsley) are present in the room when this person makes the phone call.
Correction: You also have to remember that all this took place in the dream of the female lead as evident when she wakes up and everyone "dead" is still alive and changed. For example the janitor is now a teacher.
Correction: While a majority of the cast did not act in other films, 9 of the actors (not including the 4 you mentioned) did act in at least one other film afterwards. Additionally, 1 other actor was in a film prior and 1 other actor has been in a couple shorts since.
Bishop73