Harry Potter and the Prisoner of Azkaban
How we cite our quotes:
They sat and made notes on werewolves from the textbook, while Snape prowled up and down the rows of desks, examining the work they had been doing with Professor Lupin.
"Very poorly explained [...] That is incorrect, the kappa is more commonly found in Mongolia [...] Professor Lupin gave this eight out of ten? I wouldn't have given it a three [...]" (9.4.36-7)
Snape once again wins Worst Teacher of the Year (and possibly of All Time) here. Though we have to admit: his running commentary on the students' essays is hilarious, albeit extremely mean.
"You're expecting too much of yourself," said Professor Lupin sternly in their fourth week of practice. "For a thirteen-year-old wizard, even an indistinct Patronus is a huge achievement. You aren't passing out anymore are you?" (12.5.4)
Contrast the cruel and bitter Professor Snape with the compassionate and encouraging Lupin, who teaches actual life lessons to Harry and his friends. Lupin acts as a true mentor to Harry and their scenes together shed light on nearly all of the book's major themes.