Other mistake: In season 1, we learn that Beaver is in 2nd grade-Wally in 8th. So by the end of 6 seasons, Wally would be in college. Tony Dow and Jerry Mathers are actually 2 years+/-apart.
Leave It To Beaver (1957)
1 other mistake in show generally - 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.
Captain Jack - S1-E3
Trivia: The episode "Captain Jack" was the first time a toilet was shown on TV; the boys buy a baby alligator and Wally is shown putting it in the toilet tank. The network censors were so spooked by the thought of showing a toilet on television that they delayed the episode. And when the censors finally relented, the compromise allowed only the toilet tank to be shown, not the bowl.