Reply To: In Witch He Snorted

just my hapence:

42 – he is introduced to Harry in the Leaky Cauldron as the current DADA teacher and Fred and George clearly refer to him as having taught the subject the previous year. Mareh mokom will be provided when I can get hold of a copy.

From the book:

A pale young man made his way forward, very nervously. One of his eyes was twitching.

“Professor Quirrell!” said Hagrid. “Harry, Professor Quirrell will be one of your teachers at Hogwarts.”

“P-P-Potter,” stammered Professor Quirrell, grasping Harry’s hand,

“c-can’t t-tell you how p- pleased I am to meet you.”

“What sort of magic do you teach, Professor Quirrell?”

“D-Defense Against the D-D-Dark Arts,” muttered Professor Quirrell, as though he’d rather not think about it.

[…]

“Even Professor Quirrell was tremblin’ ter meet yeh — mind you, he’s usually tremblin’.”

“Is he always that nervous?”

“Oh, yeah. Poor bloke. Brilliant mind. He was fine while he was

studyin’ outta books but then he took a year off ter get some firsthand experience…. […] never been the same since.

Scared of the students, scared of his own subject now”

It is mashma from Hagrid that he had taught DADA previously and then took off a year.Fred and George are 2 years ahead of Harry so they might have had him 2 years earlier before he took off a year. So by skipping a year he never really broke the spell – each DADA teacher only lasted a year, he happened to have come back later for a 2nd year and that one only lasted one year as well. It is dochek and I think JKR even acknowledged this in an interview at some point.