Even though the teenage stars have nothing in common with Angela Lansbury, I was irresistibly reminded of "Murder, She Wrote" while watching this film. There is a murder mystery to be solved, enough plot twists to keep the audience guessing, and resourceful detectives to ferret out the clues, just in time for the final scene, naturally. Don't expect anything too deep, and you'll have a good time watching this entertaining movie.
I don't remember too much that deserves severe criticism, but among the negatives would be that there is too much filming of the characters as they rush from one classroom to another. I expect that the director's intention was to develop a sense of urgency as the clock ticks down toward the end of period four, but there are probably more entertaining ways of building suspense than showing the actors running through the hallways.