The way school principals make sense of the context of their work shapes their actions. As in all adults, principals' sense-making capability is a function of the ego and can change over time. Adult ego development theory describes distinct, qualitatively different stages of sense-making ability. The research reported here assessed the adult ego development stage of 20 school principals in England using the Washington University Sentence Completion Test. Principals in the Self-Aware, Conscientious and Individualist stages of adult ego development were identified. The research used a critical incident technique to analyse principals' sense-making capabilities and how others experience them in their role as principals. The findings show substantive differences between those in different stages of adult ego development in relation to their sense-making processes, the feelings they experience and display as emotions, how they involve others in the sense-making process and how others experience them. There is a discernible trend in the behaviours of school principals and how others experience them that relates to the transition from the Self-Aware stage to the Conscientious stage and then to the Individualist stage. These findings have significant implications for understanding the practice of school principals.