This brief response paper seeks to clarify and expand the work of Allen and Vignoles presented in this issue. What Allen and Vignoles have done is useful because it directly replicates my earlier analyses of trends in social segregation between schools since 1989. These findings have had considerable international impact. So, to have them independently confirmed is therefore also important. The same substantive trends appear whatever sensible index of segregation is used--the clustering of pupils living in poverty in the same schools declined in the early 1990s, stabilised in the mid-1990s, and has been increasing since then. However, Allen and Vignoles appear to ignore some of the earlier findings of mine that they have replicated, and make some intriguing errors when discussing how to measure segregation, especially in relation to the properties of the Gorard segregation index (GS). (Contains 2 tables and 1 figure.)