This paper presents a new analysis of segregation between schools in terms of pupils living in poverty, for all secondary schools in England from 1996 to 2005. This shows that the clustering of similar pupils in specific schools increased noticeably from 1996 to 2001, but then settled at a level still below that of 1989 when official records began. The analysis uses four estimates of segregation using figures for take-up of, and eligibility for, free school meals compiled to create both the dissimilarity index and what has been termed the Gorard index of segregation. All four estimates give the same substantive results and the findings for the dissimilarity index and the Gorard index of segregation using either measure of free school meals are indistinguishable. The two indices are, therefore, measuring the same thing. However, the Gorard index of segregation is again shown to be more tolerant of the precise measure being used and so more strongly composition invariant than the dissimilarity index. This has important implications both for the past debate on how to measure segregation between schools and for how education authorities go about estimating segregation in the future. (Contains 3 figures, 2 tables and 6 notes.)