There is a strong association between schooling attained and test scores in many settings. If this association is causal, one might expect that programs that increase school enrollment and attainment would also improve test scores. However, if there is self-selection into school based on expected gains, marginal children brought into school by such programs may be drawn disproportionately from the left-hand side of the ability distribution, which could limit the extent to which additional schooling translates into more learning. To test this proposition, this paper uses data from Cambodia. The results show that a program that provides scholarships to poor students had a large effect on school enrollment and attendance, which increased by approximately 25 percentage points. However, there is no evidence that, 18 months after the scholarships were awarded, recipient children did any better on mathematics and vocabulary tests than they would have in the absence of the program. The paper discusses results that suggest that the self-selection of lower-ability students into school in response to the program is an important part of the explanation. The analysis also shows minimal program effects on other outcomes, including knowledge of health practices, expectations about the future, and adolescent mental health.