There are many reasons to expect that children gain something by growing up with siblings, yet there is surprisingly scant evidence of this advantage. Indeed, the vast majority of research assessing the consequences of siblings reports negative effects: Children with many siblings do not perform as well in school as children with few siblings. By focusing almost exclusively on educational outcomes, however, previous studies have neglected ways in which children might benefit from siblings. One possibility, for example, is that siblings promote children's social and interpersonal skills. In this study, we analyze a sample of kindergartners (N = 20,649) from The Early Childhood Longitudinal Study—Kindergarten Class of 1998–99 to replicate the often-noted negative relationship between number of siblings and cognitive outcomes, and then demonstrate that this pattern does not extend to social skills. Findings are consistent with the view that children negotiate peer relationships better when they grow up with at least one sibling.