Wikipedia:WikiProject Novels/Harry Potter task force/Notability/Differences/PoA

Differences from the book
Prisoner of Azkaban was, at the time of publication, the longest book in the series. The increasing plot complexity necessitated a harsh treatment of the book's finer plot lines and backstory. The connection between Harry's parents and the Marauder's map is only briefly mentioned, as is Remus Lupin's association to both the map and James Potter. Some exposition was removed for dramatic effect: both the Shrieking Shack and Scabbers the rat are mentioned only very briefly in the film adaptation, while they receive a more thorough coverage in the novel. Most of the backstory of Sirius Black is also cut, with no mention of the manner of his escape from Azkaban, his abilities as an Animagus, or the origin of the Firebolt he sends Harry.

On account of pace and time considerations, the film glosses over detailed descriptions of magical education. Only Malfoy and Harry are seen interacting with the Hippogriff during Care of Magical Creatures lessons, and most other lessons, including all of Snape's potions classes, were cut from the film. The complicated description of the Fidelius Charm is removed entirely from the film adaptation, with no explanation given of exactly how Black betrayed the Potters to Lord Voldemort. Many of the lines in this scene are redistributed amongst Cornelius Fudge and Minerva McGonagall; in compensation, McGonagall's exposition of the Animagus transformation is instead given by Snape.

Many other sequences in the film were modified from the literary counterparts to increase pace and tension. The Time-Turner sequence in particular is extended and restructured; while in the novel Harry and Hermione take great care to avoid disrupting the timeline of events, in the film version they do so several times, both accidentally and deliberately. At one point, Hermione is nearly revealed to her prior self whilst commenting on the state of her hair; at another, the pair prompt their prior selves to escape discovery by throwing stones at themselves through the window of Hagrid's hut. The embryonic romantic connection between Ron and Hermione is more prominent in the film adaptation than the original book; in response to criticism of the first two films for sacrificing character development for mystery and adventure, the emotional development of all three lead characters is given more attention in the third film. The darker side of Harry, first seen in Order of the Phoenix is glimpsed in this film, when Harry proclaims, "I hope [Black] finds me. When he does, I'll be ready. When he does, I'll kill him".