Continuity mistake: Jail cells have a rectangular slot with an outward flat extension for setting down food trays. The guard checks cells after "lights out" and there are no flat extensions for trays. (00:23:50 - 00:24:35)
Continuity mistake: Calvin sets the flowers diagonally on the desk. The stems are partly past the lower right-hand corner and one side of the roses extends past the front of the desk. The students enter the classroom, and the flowers/stems are within the desk's surface. (00:28:52)