There are perks about being born first, like getting to wear new stuff while your siblings inherit all your hand-me-downs. And according to a new study, first-born children also tend to perform better in school, have higher IQs, and be considered more accomplished by their parents.

Out of the mothers who were polled, 33.8 per cent stated that their first-born was "one of the best students in the class," and only 1.8 put their children at the bottom. And with each successive child, the former number fell while the latter rose.

But being first isn't always what it's cracked up to be. The economists who wrote the study explained that first-borns perform better mostly because parents tend to discipline their oldest the most harshly to instill fear and respect in the lower ranks of the family.
A key insight of their paper is that birth order effects arise endogenously as the result of viewing parent-child interactions as a reputation game in which parents “play tough” when their older children engage in bad behavior — tougher than caring, or altruistic, parents would prefer — in an attempt to establish a reputation of toughness to deter bad behavior amongst their younger children. Thus, we hypothesize that one mechanism that gives rise to birth order effects is this form of strategic parenting and responses by their children implied by game-theoretic models of reputation in repeated games.
Consider this as a heads up for all you "only childs" out there expecting a baby brother or sister to show up soon.

[The Atlantic]