Bobby's hair length changes throughout.
In the first shot, the Teacher is seen teaching his class. In the next shot, when the students are exiting, the Teacher, Student #2, and Student #3 are gone.
When the students leave, Bobby follows Sally out the door. In the next shot, an outside shot, Sally follows Bobby out the door.
In one shot, the Teacher is teaching his class with a camera drawn on an easel. In the next shot, there is a brain drawn on the easel.
Two different cameras appear in the film.