Tutoring Torvald / Gerald Comes Over - S1-E13
Corrected entry: In Gerald Comes Over, Gerald says whenever he goes to Arnold's house he always goes straight to Arnold's room and has never seen all of Arnold's house. Also he seems never to have met any one else that lives there, but in previous episodes we have seen him in other parts of Arnold's house and met many of the people that live there.
Correction: Other than the few episodes that take place at a certain time; this series is not meant to be taken in chronological order. Just roughly during the same 4th grade school year.