Suffer the Little Children.

Miss Sidley, an experienced, no-nonsense teacher starts to lose her bearings when she suspects one of her students, Robert, is not quite human. In a momentary reflection in her eyeglasses she thinks she may have seen Robert changing into a monster. She soon discovers that not only does Robert change, but he may not be the only one of his kind. Sidley must get rid of them before it's too late.