I Ain't Gonna Spray Lettuce No More - S4-E3
Continuity mistake: At the beginning of this episode, Cory asks Alan for money for his class photo. When Alan asks what grade Cory is in now, Cory says 11th. However, at the end of the previous season, Cory had just finished 9th grade (he and Shawn are both 15) and he spent his summer traveling the country with Eric. He should be in 10th grade, not 11th. This is further complicated later in the season, when he turns 16 and gets his driver's license. If he was in 11th grade, he would have already turned 16 and gone through driver's ed.
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.