The purpose of this study is to understand and describe patterns of principal instructional leadership practice in Iranian primary schools and to then assess whether there are differences between the high- and low-rated principals. A mixed methods design was used to collect both qualitative and quantitative data from principals and teachers within Iranian primary schools. The quantitative data were collected and analyzed from 535 teachers and 70 principals across the 70 primary schools. Next, we used ratings on the Principal Instructional Management Rating Scale to identify four of the highest and lowest performing principals. We then conducted open-ended interviews with teachers and principals in these schools. The key findings showed that, despite working in a highly centralized context, the highly ranked principals in the sample were also differentiated from their lower ranked peers on specific instructional leadership practices. They appeared to give more emphasis to their role in developing the quality of teaching and learning and monitoring student progress. In this setting, ensuring a collegial and collaborative environment for teachers is commonly articulated by the successful principals in our study as an important aspect of instructional leadership.