If you're an older sibling, then you've probably had conversations with other older siblings about how much tougher parents were on you than on your younger brothers or sisters. If you've gotten older and developed a more mature perspective, you might even have come to appreciate the idea of the sterner discipline to which you were subjected. Economists Joseph Hotz and Juan Pantano have a paper out this fall called "Strategic Parenting, Birth Order and School Performance" that both empirically confirms that parents are tougher on older children and tries to explain it in a strategic context:
Fueled by new evidence, there has been renewed interest about the eﬀects of birth order on human capital accumulation. The underlying causal mechanisms for such eﬀects remain unsettled. We consider a model in which parents impose more stringent disciplinary environments in response to their earlier-born childrens poor performance in school in order to deter such outcomes for their later-born oﬀspring. We provide robust empirical evidence that school performance of children in the NLSY-C declines with birth order as does the stringency of their parents’ disciplinary restrictions. And, when asked how they will respond if a child brought home bad grades, parents state that they would be less likely to punish their later-born children. Taken together, these patterns are consistent with a reputation model of strategic parenting.
Think about it this way. As a parent, punishing your kids has both costs and benefits. But while the cost of punishing your firstborn is basically the same as the cost of punishing a younger child (it's a hassle), the benefits of punishing your firstborn are higher because punishing the older kids has a spillover impact on the younger ones. So it makes sense to invest more in punishing the older child. But since the spillovers are not as strong as the direct effect, this means that older kids are both judged more harshly and do better in school.