Empirically, the link between classmate ability and individual-level student achievement has been established. And yet, within the scope of this body of literature, there is a dearth of studies examining if a relationship also persists between classmate ability and non-achievement outcomes--that is, social skills. This article fills this research gap. By utilizing a nationally representative longitudinal dataset from the US (i.e., ECLS-K), the effect of the percentage of classmates performing below grade level is assessed on 5 commonly accepted social skills scales. The findings indicate that kindergarten and 1st-grade students in classrooms with a higher percentage of below-grade-level classmates have greater instances of negative social skills and fewer instances of positive social skills. The results are robust across multiple methodological approaches and tests of validity. Implications for policy and practice are addressed.