Informally observing classrooms is one way that principals can help improve teaching and learning. This study describes the variability of principals' classroom observations across schools and identifies the conditions under which observations relate to the instructional climate in some schools and not others. Data for this study come from two large urban school districts and include survey responses from principals (n = 461) and teachers (n = 16,862) matched to administrative records. There is little variation in the frequency and duration of classroom observations across schools with different student demographic characteristics. There is evidence that classroom observations are not related to the instructional climate unless they are conducted with a focus on instructional improvement.