The first episode of Leave It To Beaver finds the cast knowing exactly who they are supposed to be. There is not an awkward period of time over a couple of months where they do things out of character as we have come to know them and gradually find their own lane. That could be due to the steady hand of the initial director, Norman Tolkar, who directed 31 episodes of Leave It To Beaver and later directed quite a few episodes of Walt Disney television shows, back when Walt, who knew what audiences wanted, was still alive. But I digress.
The episode finds Beaver getting a note from his second grade teacher Miss Canfield that is addressed to his mother. The other kids speak of children who got such notes and then were expelled. Beaver, determined to keep bad news away from his parents, comes up with a wild story of a house fire and a hospitalized dad to give Miss Canfield. The day after that, Wally, who will not open the letter because he considers that to be dishonest, has no problem crafting a hilarious letter for Miss Canfield that is supposed to cover all of the bases - assuming Beaver has done something bad. Instead, it just ends up looking very odd to both Miss Canfield and the principal. Complications ensue.
This show did a great job of getting inside the mind of a child, both with the exxageration of the trouble they might get into and the hilarious ideas they had for trying to get out of this imagined trouble.