The issue of social segregation in schools has seen a recent resurgence of interest – in the US, UK and internationally – as the debate rages on about whether policies that expand families’ freedom to choose amongst schools encourage divergence or convergence in the types of pupil different schools admit. Most attention has been focussed on segregation along lines of ethnic or social background. Yet, the real consideration that seems to be in the back of most people’s minds is the issue of segregation or stratification of schools along lines of pupil ability. We look explicitly at this issue using data on the population of pupils entering Secondary school in England from 1996 to 2002. Our study does highlight wide disparities between peer-group ability in different schools. But we also find that, contrary to popular opinion, almost nothing has changed over these years in terms of the way pupils of different age-11 abilities are sorted into different Secondary schools.