Teacher action and change is a complex and nuanced phenomenon that has been theorized across diverse literature in terms of identity, agency, and power. Drawing on this literature, this article offers specific articulations of teacher identity as interpretive framework, power as legitimate action, and agency as moral coherence. We posit a model of teacher agency understood in the interplay of individual beliefs, values, and ideals with institutional roles, authority, and institutional action, producing (or not producing) authentic action. This model draws a distinction between agency and power, and highlights dynamics of equilibrium and discord that may emerge between who teachers are and what they do. The agentive triad model serves as a theoretical tool for guiding or supporting teacher growth and agentive action, and for understanding the dynamics between institutionally legitimized roles and teacher identities.