As William Doherty, Brian Willoughby, and Jason Wilde noted in their recent article on the gender gap in college enrollment, “Lower academic achievement has been one of the most consistent findings in the research literature on child outcomes from single-parent families.” Kids from single-parent families have lower grades, do less well on standardized tests, and are less likely to finish high school than their peers with two parents.

And the type of family children come from appears to affect not just their own educational performance, but also that of their classmates. International data reveal that schools in which a greater proportion of students live with a single parent have lower test scores, on average, than schools in which more students live with two parents.

Jaap Dronkers, the Dutch scholar who has published several pieces on this blog about the factors linked to union (in)stability in Europe and the United States, has investigated this pattern in several scholarly articles over the last couple years. These analyses were a follow-up on the work of Suet-Ling Pong, who analyzed the effect of students’ family structure on schools’ academic outcomes in the USA only.

With coauthors Maarten H. J. Wolbers and Marloes de Lange, Dronkers first examined the mathematical literacy scores of more than 200,000 15-year-old students in 25 OECD countries, including the U.S., on the 2000 and 2003 Programme for International Student Assessment (PISA). They compared the scores of three groups of teens: those living with their mother and father, those living with a single mother, and those living with a mother plus a male guardian (like a stepfather or foster father). Other family forms were excluded because they were too rare to yield reliable results.

The type of family children come from appears to affect not just their own educational performance, but also that of their classmates.

Consistent with previous research, students living with two parents did best on PISA’s math portion. And yes, that was the case controlling for individual background characteristics, such as socioeconomic status, and the prevalence of single-parent families in their country. Here’s what the scholars discovered about the spillover effects of single-parent families:

  • There was “a strong negative relationship” between the percentage of a school’s students from single-parent families and the school’s average performance.
  • The link doesn’t boil down to school resources, school size, or students’ backgrounds, though all of those factors matter. A school’s socioeconomic composition—the average score of its students on a measure incorporating parents’ education and occupation as well as the amount of possessions in the family’s home—accounted for just half of the negative relationship described above.
  • Having lots of classmates from single-parent families hurts the math scores of children of single mothers more than the scores of children from other types of families.
  • For the most part, attending a school with many single-parent families has less of an impact on students’ performance in nations where single-parent families are more common. However, the U.S. is an exception to this rule. Despite the fact that single-parent families are more common here than in the 24 other OECD countries in the study, the percentage of an American school’s students living with a single parent remains highly relevant to the school’s scores.

In two other papers with coauthors Gert-Jan M. Veerman and Suet-Ling Pong, Dronkers tests a few possible explanations (besides socioeconomic status) for the effect of students’ family structure on school-wide test scores. Prior research by Pong suggests that social capital is one factor underlying the relationship. Schools with many students from single-parent families may be less apt to foster strong relationships among families and between families and teachers, and these relationships help parents stay informed about the school, their children’s education, and parenting in general.

Dronkers and his coauthors concentrate on another factor: classroom environment, or what they term “teaching and learning conditions.” A class made up of calm students is conducive to learning, whereas when many students regularly arrive late, make noise, and disrupt lessons, the teacher must devote more time to simply maintaining order, and has less time for direct instruction. Because children of single parents are more likely to suffer emotional and behavioral problems than other children, schools with many students in single-parent homes may have a harder time creating a learning-friendly environment, the researchers propose.

PISA data from 2009 on more than 180,000 15-year-old students in 28 OECD countries offer some preliminary evidence for this hypothesis. The higher the proportion of a school’s students living with single parents, the more classroom disruption students perceived and the lower the students’ average performance in math, controlling for socioeconomic status and several other background traits. Dronkers et al. concluded from their statistical analysis that the disruption/family structure link partially accounts for, but cannot entirely explain, the association between single-parent family prevalence and lower math scores.

Dronkers, Veerman, and Pong continue their investigation in a separate paper using 2012 PISA data (this time on some 170,000 students, again around age 15, in 28 countries). In addition to looking at the relationships between family structure, classroom disruption, and math scores, they tested the relevance of truancy, meaning how often students reported arriving late for school or skipping classes (or entire days) in the past two weeks. Higher levels of truancy were associated with lower socioeconomic status, higher levels of classroom disruption, and a greater prevalence of single-parent families in a school.

At the individual level, students living with single mothers had lower math scores and higher levels of truancy than their peers in two-parent families. Interestingly, controlling for individual truancy rendered the effect of living with a single mother insignificant, which suggests that having a single mother does not directly undermine teens’ math skills, but hurts academic performance through its impact on their likelihood of skipping and arriving late to school. At the school level, however, the average level of classroom disruption and truancy only partly explained the link between single-parent families and lower math scores. That leaves room for other theories, such as the social capital explanation.

As always, some caveats are in order. Dronkers and his colleagues emphasize that the data in the three papers summarized here are cross-sectional rather than longitudinal, and no measures were available of neighborhood quality, among other factors that may underlie the links they found. Even the measure of family structure was lacking (and varied slightly between studies), for PISA does not inquire about students’ family stability or their parents’ marital status.

Still, in the words of Dronkers, de Lange, and Wolbers, the findings imply that “[parental] divorce or separation is not only a private affair, which affects only those who are directly involved, but… also have consequences for the inequality in society and the functioning of education, one of the most important institutions of modern societies.”