Continuity mistake: In "Our Son, the Man", Greg wants his own room. One night, while in bed, Mike and Carol discuss their options. Carol says, "How about the attic?" Mike responds with, "That would be fine if Greg were only two and a half feet tall." Later, they give Greg the den for a while. However, in "A Room At the Top", after cleaning out the attic, which was now full size, both Greg and Marcia want it for their own private room.
Continuity mistake: When Jan, Marcia, and Cindy search the boys' room Cindy finds the slide projector under Greg's bed, and when Marcia holds up the transparency slide with the "ghost" image, the close-up of the slide presents two problems. First, the "ghost" is horizontal in the wide shots, but is vertical in the close-ups, and second, the fingers holding the slide in the close-up do not belong to Marcia.
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Continuity mistake: Mr. Brady places the bust on the half-wall behind the couch. When Alice swings her purse at it, it shatters immediately, but when the lights are turned on, it looks like all of the pieces are in the middle of the floor between the couch and chair.
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Continuity mistake: At the start, when Cindy walks into the kitchen she sets her books down on the counter with the book's binding facing the sink, but in the closeup the book's binding now faces the opposite way, toward the stove. Additionally, the grocery bag which was on the counter right beside Carol, has been moved for the closeup so Carol is in full view, but the bag is now at the very edge of the counter near the stove, which is pretty odd since there's not enough counter there to actually hold the full grocery bag (presumably something else supported the bag off camera).
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.
Other mistake: In one of the final scenes, Peter ignites his volcano on the patio in front of Marcia and the members of the Boosters Club. As the volcano goes haywire, Marcia and the Boosters are shrieking as the lava/mud covers them head to toe. Somehow Peter, who is much closer to the volcano, is unscathed by the eruption and remains free of any dirt.
Continuity mistake: While the kids are practising the potato sack race as Jan watches from the sidelines, when Marcia steps into her sack and hops away there's a large color image on the front of the sack, but when she reaches Peter, then turns and heads back the image has vanished - it's not on either side, then it reappears when she's back with Bobby. Additionally, when Cindy hops in the sack that Greg was in, the sack is ripped at the bottom and Cindy's feet are on the grass, but when Cindy reaches Peter the bottom of her sack is perfectly intact.
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Continuity mistake: Jennifer writes her phone number on Greg's right hand with the first number starting at his thumb, but when Greg looks at his hand to read the phone number, the phone number was written with the first number near his fingers and the last number written by his thumb.