This Sibling Tends To Be The Smartest — And Research Finally Explains Why

It's all about parental investment.

Last updated on May 16, 2025

Sibling that tends to be the smartest. Getty Images | Unsplash
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Being a firstborn child means you're the experiment. And sometimes, being the firstborn sucks big time, because occasionally you'll want to forfeit all responsibilities that come along with the title. But studies show it all seems to pay off in the end.

Two studies — one from the National Bureau of Economic Research and another from the Institute for Social and Economic Research (ISER) — have looked at how birth order affects the ability to succeed.

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The sibling who tends to be the smartest is the firstborn, and research finally explains why:

1. Firstborn children tend to excel more in school

The study from the National Bureau of Economic Research found that firstborn children excel more in school than their younger siblings. So, what exactly is creating this difference? It's all about how parents treat the firstborns.

Researchers noticed that parents' restrictions on their kids become less and less according to their birth order. (Not that we needed science to make that observation.) As a result, younger siblings' school performance declines along with birth order.

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During the study, parents were asked how they would respond if their younger students brought home bad grades, and they said they would be less likely to punish them, whereas they would have punished the firstborn. Yikes — seems a little unfair. But what doesn't kill you makes you stronger, right, firstborns?

"When parents gush over every firstborn, it motivates the oldest children to achieve," explained Psychologist Kristin Davin. "They can easily become perfectionists. They also may have trouble admitting when they're wrong. First-time parents can be overprotective and tentative while at the same time strict and demanding. This can translate to kids who overachieve."

RELATED: 11 Rare Experiences That Prove Your Sister Is Your Best Friend

2. Firstborn girls, specifically, are more likely to succeed

Smartest sibling doesn't want to overachieve PattyPhoto via Shutterstock

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ISER took it one step further and showed how firstborn girls are the ones who are more likely to succeed. Interestingly, researchers have found that firstborn girls are the most ambitious and successful children in their families. A study conducted by Feifei Bu and her colleagues surveyed 1,503 groups of siblings, which were 3,552 individuals.

This study found that "eldest daughters are an additional four percent more likely to go on to higher education than eldest sons — the next most successful sibling type." They also found that the oldest child is "Seven percent more ambitious than children born later."

The study concluded that "firstborn girls are 13 percent more likely to aspire to higher education than firstborn boys."

3. Firstborn girls might get more parental investment

Bu said, "There are several possible explanations for the higher attainment and ambition of the eldest. It could be that the parents simply devote more time and energy to them — it could be that they are more intelligent. For me, I tend to lean towards the theory that parental investment is possibly at work here."

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As the oldest child, they have more one-on-one time with their parents. So, their exclusive attention may have instilled their need to focus on themselves. Just remember, your birth order doesn't always have to end up like the most usual of circumstances. You can do whatever you set your mind to.

RELATED: The Smartest People Usually Want This Many Kids, According To Research

Nicole Weaver is a senior writer for Showbiz Cheat Sheet whose work has been featured in New York Magazine, Teen Vogue, and more.

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