A large number of studies in labor economics estimate the returns to schooling using data on monozygotic twins, under the assumption that educational attainment is random within twin pairs. This exogeneity assumption has been commonly questioned, however, but there is to date little evidence on...

Value-added models (VAMs) are increasingly used to measure school effectiveness. Yet random variation in school attendance is necessary to test the validity of VAMs, and to guide the selection of models for measuring causal effects of schools. In this paper, I use random assignment from a public...