Continuity mistake: Chet says he's spent the last year searching for his wife, but, when he left, Shawn was ending 7th grade and now Shawn is supposed to be sixteen.
Continuity mistake: When Virna is standing in the doorway of the trailer, her left arm is touching the curtains near the door. When the shot changes, her arm is instantly down at her side.
Chosen answer: In the present day, with the United States abiding by more stricter school health laws, for the most part this wouldn't be in school cafeterias as many cannot even have carbonated beverage machines now. However, in the 90s when the show takes place, it wasn't unheard of for there to be coffee machines in the cafeteria of small schools where the teachers eat with the students as we see them do often in the show. The idea being that the cafeteria was small enough so a teacher or hall monitor could catch a student before they could drink the coffee.