Continuity mistake: When Beaver makes a face for The School Picture, he sticks his tongue out. But when Mrs. Rayburn and Miss Landers are looking at the picture sometime later, Beaver isn't sticking his tongue out. (00:13:00)
Continuity mistake: At the start Ward drives up in their old 1959 Plymouth Belvedere. He had been driving the 1961 Plymouth Fury for some time in season 4.
Deliberate mistake: Although it was done for plot purposes, no school photographer would only take just one shot of a class photo. They generally take up to 15 to 20, as it is difficult to get everyone to look at the camera and smile at once (and hopefully not pull silly faces).