This report describes the 'tracking' of the EPPE 3-11 sample and then goes on to examine the possible influence of mobility on children's cognitive progress and social/behavioural development over both the pre-school and primary school period. The EPPE 3-11 project recruited children from 141 pre-school settings in six English Local Authorities (LAs) at the age of 3+. The project then followed these children through their primary school careers until the end of KS2 in primary school (Year 6, age 11). By this point the children were attending over 900 primary schools in over 100 English LAs. Tracking the sample has been an on-going process which has not just taken place at the key points of transfer for children.