STEVE INSKEEP, HOST:
School-age children will soon bring home year-end report cards. Parents may notice that one kid gets better grades than another. And they might even start to wonder, as people have for a long time, if birth order has something to do with the way that older kids do differently than their siblings.
To learn what the studies show, our colleague David Greene sat down with NPR's Shankar Vedantam.
OK, first question: Do firstborn kids do better in school?
SHANKAR VEDANTAM, BYLINE: You know, David, there's been debate about this, but there does seem to be evidence that firstborn kids do better in school. They seem to also earn more in their lives. More presidents and Nobel Prize winners are more likely to be firstborn kids or only kids. Now obviously, your birth order doesn't determine everything. These are patterns that you see on average. Your life outcomes are not shot if you're not an oldest kid.
DAVID GREENE, HOST:
Well, and I guess I can imagine parents having more time to devote to firstborn kids. I mean, once kid No. 2 arrives, 3 comes along - I mean, parents start to get worn thin.
VEDANTAM: That's right. That's the resource's explanation for the phenomenon, David. And it's interesting, different academic disciplines have come up with different models to explain the same data.
VEDANTAM: There was an earlier study that looked at how parents divide their time equally among all their kids. But what that ends up meaning is that the first-born kid ends up getting more time just because there were no competitors at that point. There's a theory from education that suggest that first-born kids are often in the role of playing mentor or teacher to their younger siblings, and the experience of being a mentor itself is what is producing the outcomes.
GREENE: A lot of forces might be at work here.
VEDANTAM: Right. Now, what we have that's new is a model from economics. Joseph Hotz, at Duke University, and his co-author, Juan Pantano, have suggested that the reason this is happening is that parents want all of their kids to do well. But there's two different ways you can do this. You can try and ride herd on all of them, but it's very costly and expensive to do. And so parents come up with a strategy. They focus on the oldest kid because that serves as a signaling mechanism to all the other kids.
JOSEPH HOTZ: Make, if you will, an example of your oldest child, saying to them: If you come home with poor grades, we're going to restrict your television watching; you're going to be doing your homework every night after dinner. There are two things that happen there. One, it affects that child, right? They get the message. But so do their younger siblings. Hey, Mom and Dad mean it; they really are going to punish us if we don't do stuff.
GREENE: Shankar, I find myself thinking here about police officers who can't pull over everyone who is speeding. But they hope that when they do pull over a motorist that other drivers out there are going to see that and get the message.
VEDANTAM: That is exactly the same model that Hotz is applied to parenting, David. And his point is, regardless of the effect on the spectators, the poster kids really responds to your intervention. The driver starts to really slow down, the oldest kid starts to really shape up.
I asked Hotz what the evidence was for this model. You can't conduct controlled scientific experiments involving parenting. So what Hotz did was, he looked at survey data that asks parents each time one of their children turned 12, how upset would you be if your kid came home with bad grades. And what he found is that systematically, parents were more upset when their oldest children came home with bad grades.
GREENE: If that 12-year-old was the oldest child, at that point.
VEDANTAM: Exactly. And they were much more likely to restrict television watching, much more likely to focus on the kid's homework, but only for the oldest kid. With subsequent children, they significantly eased off the pedal. Hotz also said he has another data source, and that's his own family. Here he is.
HOTZ: I have two siblings who are older than I am, and two siblings who are younger than I am, so I'm smack-dab in the middle. And when I started working on this research, my oldest sister, you know, clearly claimed she was parented differently. She said, you know, she didn't get away with anything when she was growing up. And as we all agree, my youngest sister got away with everything.
GREENE: Shankar, I mean, are parents making decisions consciously here to ease up on the gas with second, third, fourth children?
VEDANTAM: You know, it could be that they're doing it. It could be that this is happening unconsciously. They say we really focus really hard on the first kid; we're going to ease up on the others. It could be that younger kids are just testing the boundaries and they find that after some time, parents are not really hard-core.
GREENE: And I guess you used the term earlier, costly. It costs a lot, in terms of sort of emotion and energy, to be a disciplinarian.
VEDANTAM: It does. And, you know, I almost hate to say this because kids might be listening to the program right now, David, but parents actually don't really want to be disciplinarians because it's very costly, it's very unpleasant and frankly, parents have better things to be doing with their time.
GREENE: You speak from personal experience, Shankar.
VEDANTAM: I do indeed, David.
GREENE: Shankar, thanks for coming in, as always.
VEDANTAM: Thank you.
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INSKEEP: His kids - well-behaved. I don't know how that worked out. Anyway, Shankar Vedantam regularly joins us to talk about social science research. You can follow him on Twitter @HiddenBrain, and follow this program @MORNING EDITION, @ nprinskeep and @nprgreene. Transcript provided by NPR, Copyright NPR.