Continuity mistake: If you look in most of the scenes, especially the one where she is throwing the stuff out the window, you can see a wall out of the window, but in the scene where Cory comes back from seeing the lady you can see a dresser out the window.
Continuity mistake: When Cory is whispering in Amy's ear, she is holding a cup of frozen yogurt in her left hand. When the shot changes, she is holding it in her right hand. (00:16:40)
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.