When Barbara Ann inscribes her name in cement near beginning of film, she writes the second R in first name twice due to inconsistency in long shot and closeup.
Plant Skills teacher Mr. Beverly describes flower pollination backwards. It is the stamen which produces pollen that the pistil then receives, not the other way around, as he phrases it.
In one of the rooftop scenes, the boom mike is clearly visible.
In the scene when McDowall is recording his story, the shadow of a boom mic can clearly be seen bobbing on the wall behind his head.