"Ability" is one of the most common concepts underpinning education. Generally, "ability" is central to notions of a meritocratic society. More specifically, schools are allocated the right to define, categorise and label students according to their ability. While there has been ample discussion of the role of ability in the creation of curricula, teachers' concepts of "ability" have remained relatively unstudied. Using semi-structured interviews with 236 primary and secondary school teachers, we examined how teachers use concepts of "ability", identify its conceptual components in their discourses (its anatomy), and show how the internal structure of the concept relates to specific institutional functions. Teachers' uses of "ability" prompted us to recount a too-often forgotten perspective--the reframing of our understanding of schools as institutions. Recognising the internal anatomy of ability, as it is used in schooling, helps us better understand its capacity to survive within a broader ecology of schooling, and the degree to which schools are designed to limit learning and legitimise consequent social exclusion.