Principals are increasingly expected to be the instructional as well as administrative leaders of their schools. However, little is known about how principals reason through the instructional issues that they face. An analysis of principal reasoning in instructional contexts is critical. The study presented in this article draws on interviews with 36 predominantly elementary school principals in an urban setting. The authors look at principal problem-solving by comparing the cognitive processes that principals of varying degrees of expertise use in solving instructional scenarios. This quantitative approach tests the hypothesis that expert principals use more expert processes and typical principals use more typical processes. The results confirm that expert principals relied more on gathering data across all instructional scenarios and spent more time following up on their solutions when solving problems in the mathematics domain. Typical principals were more likely to share anecdotes that were negative or unsuccessful in nature across all domains. (Contains 16 figures and 16 tables.)