The Effective Pre-school, Primary and Secondary Education Project (EPPSE) has investigated the cognitive and social-behavioural development of approximately 3,000 children from the age of 3+ years since 1997. This Research Brief focuses on the relationships between a range of child, family, home, pre-, primary and secondary school characteristics and students' social-behavioural development in Year 9 at secondary school (age 14). It compares these latest findings with those found for social-behavioural development at younger ages, highlights the specific influences of secondary school on students' social-behavioural outcomes in Year 9 and changes in these developmental outcomes between the ages of 11 and 14. The social-behavioural development of young people is important in its own right because it contributes to well-being, but also because it can influence current and future academic achievement, and shape developmental pathways. EPPSE derived four measures of social behaviour from individual student assessments made by teachers. These are 'self-regulation' (problem-solving, motivation, self-confidence, assertiveness etc.), "pro-social behaviour' (peer empathy, co-operation, altruism etc.), 'hyperactivity' (reduced self-control, impulsiveness etc.) and 'anti-social behaviour' (verbal abuse, aggression etc.).