In this article, the author describes how four seasoned Chicago educators keep their teaching fresh. He learned that none of them do quite the same thing in the classroom twice, and none teaches like the other. They do, however, have one key trait in common: they are self-propelled. Their best source of professional development is not a mandated chalk-and-talk or some perky pep rally, but their own curiosity. They are always looking for new ways to approach subjects and present material. They analyze students and their parents. They tear apart each lesson and look for the weak spots. They have each found a unique formula for making their teaching not just as good as it ever was, but better than it has ever been before.