Full Moon / Student Teacher - S4-E1
Other mistake: Full Moon: When Arnold tells Sid, Stinky, and Harold that he was given four weeks' detention, Harold tells him to not rat on them. Arnold says he won't tell, and when he walks away, his hair passes right through Sid's head. (00:03:30)
Answer: The show is based in present day times. Plus most cars aren't old fashtioned, I recall seeing a limo and not to mention a cherry picker, etc.