Research brief: The Effective Pre-School and Primary Education 3-11 project (EPPE 3-11) investigates the impact of pre-school provision on a national sample of young children in England between the ages of 3 and 11 years. This Research Brief focuses on the relationships between various child, family, home, pre-school and primary school characteristics and measures of children's social/behavioural development collected at age 10 in Year 5 of primary school. It compares the findings at age 10 with the influence of the same factors when the children were in Year 1 (age 6). The Brief also reports findings about the combined influence of pre-school and primary school experience on children's social/behavioural development in Year 5. Four dimensions of social behaviour were identified based on teachers' ratings of children in the sample: 'Self-regulation', 'Pro-social' behaviour, 'Hyperactivity' and 'Anti-social' behaviour.