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Low grades, bad behavior? Siblings may be to blame, FSU study says

We all know the story of a man named Brady and the group that somehow formed a family. But if the iconic '70s sitcom about a "blended" family reflected reality, the Brady Bunch likely would have been dealing with much more than silly sibling squabbles.

Kathryn Harker Tillman

Here's the real story: On average, adolescents living with half- or stepsiblings have lower grades and more school-related behavior problems, and these problems may not improve over time, according to Florida State University Assistant Professor of Sociology Kathryn Harker Tillman.

"These findings imply that family formation patterns that bring together children who have different sets of biological parents may not be in the best interests of the children involved," Tillman said. "Yet one-half of all American stepfamilies include children from previous relationships of both partners, and the majority of parents in stepfamilies go on to have additional children together."

Many studies have focused on the structure of parent-child relations in connection to academic achievement, but Tillman's study is unique in that it focuses on the composition of the entire family unit. Tillman studied data from the National Longitudinal Study of Adolescent Health, a nationally representative study of more than 11,000 adolescents in grades 7 through 12 in the United States. Her study is published in the journal Social Science Research.

All stepfamilies are not equal—at least in terms of their impact on children's academic performance. Surprisingly, teens who live in the most seemingly complicated family arrangement of all—those with both half- and stepsiblings—fare better than those who live with only stepsiblings or only half-siblings. Tillman theorized that perhaps the decision of the parents in these families to have a biological child together reflects a stable relationship or one in which child rearing is especially important. Only 1 percent of youth in Tillman's study lived in this so-called complex blended sibling composition, however.

Boys living with half- or stepsiblings appear to have the hardest time coping, with average GPAs one-quarter of a letter grade lower than boys who live with only full siblings. Girls with half- or stepsiblings also had lower GPAs than those living with only full siblings, but the difference was much smaller. Boys and girls in these types of families also had more school behavioral problems, such as trouble paying attention, getting homework done and getting along with teachers and other students.

Tillman looked at how long children had been living with their half- or stepsiblings and found that it didn't really matter. Things did not tend to improve with time.

"We cannot assume that over time, children will naturally 'adjust' to the new roles and relationships that arise when families are blended," she said. "This research indicates that the effects of new stepsiblings or half siblings may actually become more negative over time or, at the least, remain consistently negative."

Part of what makes stepfamily life difficult for young people is the complexity, ambiguity and stress that come with having nontraditional siblings living in the same home, she said. Stepsiblings who are living together may also engage in, or at least perceive, more competition for parental time, attention and resources than full siblings.

In addition to stressful life changes and ambiguous family roles, stepfamily formation leads to the introduction of a new parent-figure who may be less willing or able to invest in a child's development and academic success, Tillman said. Stepparent-child relationships tend to be more conflict-ridden than relationships with biological parents, and stepparents tend to offer children less parental support, closeness and supervision. The presence of a stepparent also generally leads to a decline in the amount of attention and supervision children receive from the biological parent with whom they live.

Furthermore, stepparents generally report feeling less of an obligation to provide financial support for stepchildren's postsecondary education, and both biological parents and stepparents report actually providing less support for children's education when they are living in a stepfamily.

"Lower social and financial investments may signal to children a lack of parental interest and lower expectations for academic achievement and college attendance," she said. "In turn, youth in stepfamilies may be less likely to get academic assistance when needed, less likely to work for higher grades and more likely to act out at school."

By Jill Elish


"These findings imply that family formation patterns that bring together children who have different sets of biological parents may not be in the best interests of the children involved."

Kathryn Harker Tillman
FSU Department of Sociology