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).
Leave It To Beaver (1957)
1 deliberate mistake in season 4 - chronological order
Starring: Barbara Billingsley, Hugh Beaumont, Jerry Mathers, Tony Dow
Visible crew/equipment: The shadow of the boom mike is visible in the background when Wally is saying that June looks "ritzy". (00:14:45)
June Cleaver: Dear, do you think all parents have this much trouble?
Ward Cleaver: No, just parents with children.
Trivia: Phyllis Coates, who plays the new neighbor Mrs. Donaldson, played Lois Lane in the first season of the Superman TV series in the 1950s.