Most research on the consequences of the number of siblings highlights their downside—the negative association between sibship size and educational outcomes. But recently scholars have begun to understand the potential benefits of siblings, with some research indicating that kindergartners are more socially adept when they have at least one brother or sister. We expand this line of inquiry by studying fifth graders, a point where sufficient school-based peer interactions have occurred to potentially eliminate the social skills deficit observed among only children beginning kindergarten. Analyzing 11,820 children from the Early Childhood Longitudinal Study—Kindergarten Cohort of 1998-99, we find that, contrary to our expectations, only children failed to gain more social skills between kindergarten and fifth grade than their counterparts with siblings. This pattern has important implications for the one in five children now raised without siblings.