Continuity mistake: As the family is sitting at the breakfast table during one of the very first scenes, Beaver gets up to leave for school. The checkered napkin in his lap falls to the floor as he walks to the back door. The camera cuts back to the table where the napkin has magically reappeared.
Continuity mistake: There are a couple of continuity errors in the dance scene: First, the 4 girls sitting across from the boys switch positions from one shot to the next, then the last girl (long dark hair) disappears from the row of girls entirely, only to show up on the dance floor later in the scene. She was across from (and should have been paired up with) Beaver; instead, the teacher nods toward a now-empty chair and remarks that they "ran out of girls".