In this essay, Eleanor Drago-Severson and Jessica Blum-DeStefano add a new dimension to the literature on social justice in education and constructive-developmental theory by exploring how adult developmental theory can shed new light on the challenges and opportunities of teaching and leading for social justice. Drawing from their decades of research and teaching about leadership that supports educators' internal capacity building, they posit that adults' qualitatively different ways of knowing--or developmental meaning-making systems--will influence how they understand diversity of all kinds, as well as what it means to teach and/or lead for social justice. Given the imperatives of equity and access in educational institutions, US society, and the world, this essay aims to help us better understand how to support diverse adults in their efforts to serve all students well and to work more collaboratively and productively across lines of difference.