This article presents an analysis of the association between pupil mobility and educational attainment in the 2002 national end of Key Stage 2 (KS2) tests for 11-year-old pupils in an inner London education authority. The results show that pupil mobility is strongly associated with low attainment in the end of key stage tests. However, the negative association with pupil mobility is reduced by half when account is taken of other pupil background factors known to be related to educational attainment (such as special educational need and socio-economic disadvantage), and is eliminated entirely when account is also taken of pupils' prior attainment as indicated by end of KS1 test scores at age 7. Thus there is no indication that changing schoo...