Chapter 6: The Adventures of Eustace

How did Eustace turn back into a boy?

Eustace was able to make himself hard-hearted and selfish, but he's not able to strip away his outer "shell" and get back to his true nature on his own. For that he needs Aslan's help. Aslan seals Eustace's transformation from a dragon back into a boy with a baptism-like dunking in a miraculous pool.