"Ever go into another room for something and then forget what you were there for? A new study suggests that simply passing through a doorway can cause you to forget why you came into a room or what you wanted to find.(You can read the rest of the article here.)
'Entering or exiting through a doorway serves as an "event boundary" in the mind, which separates episodes of activity and files them away,' Gabriel Radvansky, a psychology professor at the University of Notre Dame, said in a university news release."
So I guess coming in and out of my classroom erases my students' memories. This explains a lot.