We explore the relative influence of family and neighbourhood on pupils' test scores and how this varies by sibling type. Using English register data we find that the neighbourhood explains at most 10–15% of the variance in pupils' test scores, whereas the variance explained by family is between 44% and 54% at the end of primary school and between 47% and 61% at the end of compulsory schooling. The family influence is significantly higher for identical twins. It is also higher for dizygotic twins than for non-twin siblings brought up at different times and therefore experiencing varying family circumstances.