Anti-Dementor lessons

"A Patronus is a kind of positive force, and for the wizard who can conjure one, it works something like a shield, with the Dementor feeding on it, rather than him. In order for it to work, you need to think of a memory. Not just any memory, a very happy memory, a very powerful memory… Allow it to fill you up…lose yourself in it…then speak the incantation ‘Expecto Patronum’."

- Remus Lupin

In 1994, Remus Lupin, then-Professor of Defense Against the Dark Arts offered to teach Harry Potter how to perform a Patronus. The class took place in the History of Magic classroom. The way they did the class was that they got a boggart and when the boggart saw Harry, it would take form of a dementor. Harry would, then, practice on the dementor. Harry would eat chocolate after each lesson.

These lessons between Harry and Remus began just after the Christmas holidays.