UNIVERSITY PARK, Pa. — The effects of sibling relationships may go beyond childhood bickering and bonding, according to Penn State researchers who found that these relationships may predict similarities and differences in siblings’ education later in life.

In a study spanning about 15 years, the researchers found that when siblings felt more warmth toward each other in childhood, they were more likely to achieve similar levels of education. But, when siblings felt that their parents’ treatment of themselves versus their sibling was unfair, or when their fathers spent more time with one sibling than the other, those siblings achieved different levels of education.

Xiaoran Sun, a doctoral candidate in human development and family studies, said the results held up even when the researchers controlled for the siblings’ grade-point averages across childhood and adolescence, suggesting that school achievement may not be the only factor determining what level of education a person achieves.

“While school is obviously important, this study helps show that what goes on inside families can have an impact, as well,” said Susan McHale, distinguished professor of human development and family studies. “Warmth from siblings may not mean you’re more likely to go to college, but it seems to be a factor in how similarly the two siblings turn out. People don’t tend to think about siblings being important to academic achievement, but our findings highlight the importance of family experiences — beyond what happens at school.”

Previous research has shown that graduating college has an impact on an individual’s employment, health and the way they form families of their own. While it’s been shown that parenting can affect educational achievement, little work has been done to study whether siblings have an effect.

“A lot of research on child development focuses on one child in the family, with the assumption that if you know what happens to this one child, you know how families operate to socialize children,” McHale said. “But in the U.S. and elsewhere around the world, more children grow up in a home with a sibling than with a father figure. So by studying siblings, you start to get a better sense of the larger family context of development.”

The researchers followed the two oldest siblings from 152 families from middle childhood through their mid-twenties. The families lived in central Pennsylvania and were mainly European-American.

When the siblings were an average of 11.8 and 9.2 years old, the researchers measured warmth by asking the children questions, like how often they turned to their sibling for advice or support. Additionally, the researchers gathered data on whether the parents treated their children differently, and whether the siblings thought this different treatment was fair or not. They also measured how much time the siblings spent alone with their mothers and fathers.

When the siblings were around 26 years old, the researchers followed up to ask each sibling about their highest level of completed education.

“The sibling relationship factors that we tested did not predict whether an individual sibling would graduate from college or not, but we did find predictors of whether siblings would achieve different levels of education,” said Sun. “The findings provide clues about how sibling relationships can affect education pathways.”

The researchers said there are a few possible explanations for the findings, which were recently published in the journal Child Development. Sun said that when siblings feel more warmth for each other, they have a closer relationship in general, and thus may be more likely to follow similar paths in their education achievement.

“When two people are closer to each other, they tend to treat each other as role models,” Sun said. “And this could be for better or for worse. They can be 'partners in crime,' as some prior work suggests, or partners in achievement, as we found. It’s not that siblings who are close are more likely to graduate from college, they’re just more likely to end up with the same level of education, either graduating from college or not.”

McHale said that for the siblings who ended up with different levels of education, the perception of their parents treating them differently and unfairly may have been part of what drove their different choices.

“Children are vigilant in noticing how they're treated relative to their siblings, and parents need to be aware of this and on their guard,” McHale said. “Many parents treat their children differently and have very good reasons to do so, but children need to understand parents’ reasons, and parents have to have conversations with their children to explain those reasons. If kids perceive their treatment as fair or justified, even if it’s different from their siblings’, then there's not the same negative effect.”

Sun said the results could help design future interventions that focus on siblings. The researchers said that it may be helpful to design studies that could explore the possible causal role of sibling relationships on education, as well as studies of more diverse populations.

This work was supported by the National Institute of Child Health and Human Development.

Kimberly A. Updegraff, Arizona State University, also participated in this research.