Explaining Sibling Differences in Achievement and Behavioral Outcomes: The Importance of Within- and Between-Family Factors

Most research on child behavioral and cognitive outcomes focuses on the impact of variables measured across families—holding a number of other characteristics constant. However, this research is limited in that it does not capture variation in child developmental outcomes that occurs within families. To address these limitations, we examine correlations of child outcomes between siblings from the same family. We conduct this analysis for several demographic subgroups. Furthermore, to better understand how these inequalities are generated within families, we also examine the impact of individual level characteristics within families using fixed effects models. Results from our between-family analyses indicate that siblings with fewer family resources are more similar on behavioral outcomes compared to siblings in more privileged families. However, children in two-parent households perform more similarly on age-adjusted achievement tests than do children in single parent households. Results from our within-family sibling comparisons reveal that first born children generally outperform their younger siblings on age-adjusted achievement tests.