First in the class?

"Older children outperform younger children in a school-entry cohort well into their school careers. The existing literature has provided little insight into the causes of this phenomenon, leaving open the possibility that school-entry age is zero-sum game, where relatively young students lose what relatively old students gain. In this paper, we estimate the effects of relative age using data from an experiment where children of the same biological age were randomly assigned to different classrooms at the start of school. We find no evidence that relative age impacts achievement in the population at large. However, disadvantaged children assigned to a classroom where they are among the youngest students are less likely to take a college-entrance exam than others of the same biological age. Controlling for relative age also reveals no long-term effect of biological age at school entry in the aggregate, but striking differences by socioeconomic status: Disadvantaged children who are older at the start of kindergarten are less likely to take the SAT or ACT, while the opposite may be true for children from more advantaged families. These findings suggest that, far from being zero-sum, school-entry age has far-reaching consequences for the level of achievement and achievement gaps between the rich and poor"--National Bureau of Economic Research web site.