This article extends our understanding of early school leaving in developed countries by analysing whether the risk of dropping out depends on family characteristics such as number of siblings and birth order. The study is based on a large sample of the 2011 Spanish census and estimates the relative risks of early school leaving using Poisson regression models. The main findings point out that the risk of dropping out of school is negatively related to both the number of siblings and birth order. Moreover, this negative relationship appears across virtually all socioeconomic statuses. Only families in high social positions manage to mitigate the impact of the number of siblings, but not that of birth order.