This article presents a social constructivist grounded theory of school principal legal learning. The author analyzed 10 interviews with K-12 school principals and 10 school law faculty documents to investigate how principals develop the knowledge and skills to address legal issues in schools. Two themes emerged. The first theme was source of legal learning, with categories that included theoretical legal learning and practical/reality-based learning. The second theme was supports for legal learning, with categories that included supports of school law faculty, attorneys, policies, building level--specific content, professional development, and a combined practice of reflection to develop a common-sense approach.