In this qualitative study, we applied the concept of expert noticing to instructional leadership in high-performing urban schools that attained both excellent and equitable results for the various diverse populations they served. Unlike the overwhelming majority of urban schools in the United States, in the schools we studied, the academic achievement of African American, Latino, and low-income students exceeded state averages for all students. Assuming that principals who influenced the growth of these high-performing urban schools might be considered experts, we sought to understand what these experts noticed about classroom instruction. Given the exploratory nature of this inquiry, a qualitative interview study was chosen as the method of inquiry. We interviewed 14 principals of some of the nation's highest performing urban elementary, middle, and high schools. The principals consistently reported that, as they observed classrooms, they noticed concerns related to student engagement and understanding and classroom atmosphere. In particular, principals paid attention to the extent that students were talking, explaining, and describing in ways that gave teachers an indication of each student's levels of understanding of the lesson content. Similarly, principals noticed the climate, atmosphere, or tone of the classroom. The priorities that principals claimed to notice were different from those that principals are often taught to observe through preservice and in-service training, generating important questions and opportunities for further study.