What does scout learn from Boo Radley?

Scout learns not to judge people from the outside, as she had done her entire life. Or, not exactly the outside, since she had never seen Boo. But she had assumed the worst of Boo due to rumors and gossip. In the end, standing on his porch, she 'walks around in his skin', and finally realizes that she and the town had been wrong about him. Boo is really kind, quiet, and brave in his own way. She learns that bravery comes in unexpected forms, not to judge someone by what everyone else says about them, and that people have their own reasons for the things they do- she has no right to judge until she knows those reasons for sure.