It could be the case that parents are more relaxed with their later-born children because they are exhausted and less anxious about policing their children's behavior. – Deni Kirkova

Older children perform better academically in school than their younger siblings, a fact that new research says may boil down to differences in how strictly they are parented.

Study authors V. Joseph Hotz of Duke University and Juan Pantano of Washington University found parents are more enmeshed in the academics of their oldest children and are more apt to create strict rules — and to exact punishments for poor performance.

"It could be the case that parents are more relaxed with their later-born children because they are exhausted and less anxious about policing their children's behavior," Deni Kirkova of the Daily Mail said in a report about the study.

Hotz and Pantano found that parents are more stringent, both in expectation and in discipline, on their first children, then loosen up as they have subsequent children. Because of that, older children get better grades.

"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," they wrote. The duo acknowledge that their evidence is primarily based on perceptions of school performance, but they validated the perceptions by looking at transcripts and found the same thing. After they controlled for measures of a child's ability taken at earlier ages, "birth order effects in school performance persist."

The researchers also tried to control for things like family disruptions such as divorce and impacts they might have. Again, they found a birth order effect. Other studies suggest possible reasons for birth order effects. In this study, they round up several possibilities, from parents spending more time with a first baby and thus helping intellectual development, to lower-quality genetic endowments and the possibility that how first-borns and their parents interact may determine whether parents decide to have second-borns at all.

Perhaps, it is noted, a last-born misses out on the benefits of teaching younger siblings. Or a later-born is more likely to have lived with divorce or other disruptions. It's also possible that parents get lazier or less focused as they have more children.

That's the one that resonates with mommy blogger Jacqueline Burt. She summed up her thoughts in the headline of a post she wrote on the study for The Stir at "Firstborn Kids Are Smarter Because Parents Are Tired, OK?!"

According to the researchers, that's not it.

"In particular, earlier-born siblings are predicted to put more effort in school and should end up performing better. Moreover, parents are more likely to establish rules of behavior with the earlier-born, engage in a more systematic monitoring of earlier-born's schoolwork and increase supervision in the event of low school performance. … We provide evidence on the validity of these predictions of children's performance in school and parental responses to it by birth order," they wrote.

"The theory is interesting but not entirely persuasive," wrote Derek Thompson in The Atlantic. "First, it seems nearly impossible to test. The survey data is much better at showing that parents chill out as they have more kids than at showing that parents chill out because they're explicitly establishing a reputation for strictness. Nothing in the paper seems to argue against the simpler idea that parents seem to go soft on later kids because raising four children with the same level of attention you'd afford a single child is utterly exhausting."

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