On the surface, nearly everyone knows what goes into good teaching: knowing the subject matter, knowing and relating to the students, appropriately implementing a good curriculum, and knowing how to manage the classroom and students. Most citizens believe they know a lot about teaching, having spent 8 or 12 or many more years in classrooms with teachers. Then, if they get a chance to be a “teacher,” especially in the precollege classroom, they find the situation to be a whole lot more complicated than they expected. So, what makes good teaching so difficult? What are the elements of professional expertise in teaching, and how can that expertise be engendered in preservice and inservice teachers?