Measuring “good teaching” in consistent and fair ways, however, is not easy. One reason is that teaching is not static. How a teacher teaches varies depending on the instructional content and the goal of a lesson. For example, we might want to see extended discussions among students in some lessons and more teacher-focused instruction when introducing new content. Student-teacher interactions also evolve over the course of a school year. Yet, most teachers are only observed one or two times a year. The dynamic nature of instruction makes it challenging to characterize one’s teaching from only a few lessons. Even if these observed lessons can capture one’s “typical” or “average” teaching, feedback based on such information might not be that useful, as what a teacher needs to support students in November may well be distinct from that same teacher’s need in May.