Visible crew/equipment: When Mike and Bobby drive up in the station wagon, just as Mike stops the car, on the left side of the screen we can see the edge of the house set. Instead of the usual wood fence in the yard, there appears to be a directors chair (provided to all cast members) in the dark background. (00:05:35)
Continuity mistake: When Marcia takes her last turn placing a card at the top of the tall house of cards, in the shots facing her she's stressed about accidentally collapsing the cards so she holds back her charm bracelet with her left hand, but in the first shot facing the three boys Marcia's left arm is down at her side and the charm bracelet is dangling at her wrist, right beside the cards. (00:21:00)
Deliberate mistake: During Peter's party, when the girls start to gather around Peter to try and convince him that he's not dull, there's a closeup of Peter that's a flipped shot. Additionally, when everyone runs out for the fire drill, Peter's striped tie is tied very differently - it goes from grey/gold at the top to burgundy at the top.
Continuity mistake: When Jan's in the backyard checking on the cloud and moon set decorations being painted by Marcia and Cindy, there's less "dark and gloomy" paint actually painted on the cloud after Cindy stands up with the smiley moon. (00:06:20)