Teacher's Pest

S5, E22: The Powell children are tired of having to go places with their grandfather, so they get Charles to convince Walter to take a history class at the college where Charles is an assistant teacher. The next day, Walter shows up for class and listens to Charles lecture on World War II, correcting Charles on his facts, then informs the class he will give them private lessons. Now that Walter has found a new interest, the Powell children feel they are being ignored because Walter has no time for them.