When Ward and June come up to the boys' room, Wally and The Beaver are cleaning up. Wally picks up a set of roller skate wheels and balances them on his left shoulder while Ward is telling him he will be studying for his history exam, not going out with the guys. The skate wheels remain in view until the cut to Ward's last line of dialog, when the skate wheels suddenly are no longer on Wally's shoulder.
When Beaver and June are washing the dishes after supper, the long shot shows a percolator on the counter next to the stove, and a large pot on the stove. In the shots of just Beaver, the pot and percolator are missing.
The test score sheet posted on the high school bulletin board misspells Clarence 'Lumpy' Rutherford's first name as "Clarance". Considering that a school teacher typed the names on the test score sheet, this is an egregious error.
When Wally gets up to wash the ink off his hands, he hasn't wiped them on anything and his fingers are dripping ink. Yet he carelessly opens and closes the door by grasping the doorknob barehanded. This is very out of character for Wally.