The aims of this working paper were to investigate whether taking part in out of school activities during primary school is linked with end of primary school attainment and social, emotional and behavioural outcomes, for all children and specifically for children from economically disadvantaged backgrounds. The analysis is based on the Millennium Cohort Study (MCS) survey data linked to administrative data holding the cohort children’s Key Stage 1 (KS1) and Key Stage 2 (KS2) attainment scores. In addition to looking at KS2 attainment (total point score, English and maths) the authors also investigated social, emotional and behavioural outcomes using the Strengths and Difficulties Questionnaire (SDQ) total difficulties and prosocial skills scores. The results presented in this paper are based on logistic and multiple linear regression analysis. Results showed that sports clubs and ‘other’ (unspecified) club participation was positively associated with attainment outcomes at age 11, when controlling for prior attainment. Participating in organised sports or physical activity was also positively linked to social, emotional and behavioural outcomes. Among disadvantaged children, after school club emerged as the only organised activity linked to child outcomes; participation was linked to both higher KS2 attainment and prosocial skills. The implications of these findings for further research, policy and practice are discussed.