Executive SummaryPupil mobility has become a key issue in recent British policy debates in education. The government is paying more attention to issues surrounding the extent and patterns of pupil mobility because of its potential impact on pupils' academic attainment, on their future contribution to society, on the schools they belong to, and the implications for the evaluation of school performance. However, despite this increasing emphasis, empirical analysis on the determinants of pupil mobility has been thin on the ground, especially in the UK context. This is particularly true at the national level, as most of the existing research focuses on pupils in specific LEAs or considers specific birth cohorts of children.In this study we offer an empirical analysis of the extent of and patterns in pupil mobility for all state school children in England. We exploit a large administrative longitudinal data source -the Pupil Level Annual School Census (PLASC) -for two academic years, 2001/2002 and 2002/2003. These data offer significant advantages because of their coverage of all state school pupils in every year of compulsory schooling. We measure pupil mobility on the basis of whether there is a change in the school that a pupil attends between two academic years. Another advantage of PLASC is that we are able, for the first time, to look at mobility patterns not only in terms of schooling, but also look at simultaneous changes in home residence.Our results show that 4.4 percent, or around a quarter of a million, of pupils make noncompulsory moves in the period of study. Our key findings are that: pupils from lower social background are more likely to switch schools than other pupils, and this is true for pupils at all stages of schooling; pupils who change schools are more likely to have a low previous academic attainment record than pupils who do not change schools; pupils placed in schools with high Key Stage performance levels move less than pupils from lower performance schools; pupils who move school and home simultaneously are typically more socially disadvantaged than otherwise; pupil mobility is more marked in London than in other regions of the country; and children who move are more likely to enter a school with better Key Stage performance than the one they left, although this improvement is significantly more marked for children from better off background.