Education systems are made up of individuals, groups, identities, cultures, institutions, discourses, networks, histories, relationships, and so on. In other words, educational systems are complex. Enter into this complexity the issue of inclusion from/for a heterogenous society and how these complex systems can be designed and -- specifically for our purposes -- analysed. In this article, we propose a new conceptual framework for assisting in the understanding of inclusion in complex educational systems: Complex Educational Systems Analysis (CESA), and its visual representation via the CESA Cube (CESA3). At the very heart of CESA is the question of educational purpose. Why school? What is education for? These questions have direct implications in how we understand educational systems and, indeed, how we understand inclusion within these systems.