I remember watching a film about a boy that moves in with his mum next door to this boy who is in a wheelchair, and tries to befriend him but he doesn't like him, then they start hanging out and at some point there is a crash with a school bus? At the end the boy in a wheelchair dies and it shows the boy reading the story from a book? What film is this?

The Mighty, although there is no school bus crash. That does happen in the movie Simon Birch.