Objective This study examined whether birth weight variation within the normal range was associated with language ability at 36 months, and whether responsive parenting—the putative protective factor—buffered children from the risk of relatively low birth weight. Methods In all, 467 community mother–child dyads were followed longitudinally from birth. Receptive language was measured at 36 months. Responsive parenting was assessed through observed interactions at 18 months and examined as the hypothesized moderator. Results Controlling for confounds, both birth weight and responsive parenting positively predicted children’s language skills. There was also a significant interaction between birth weight and responsive parenting—higher responsivity was associated with better language ability, and this link was especially pronounced for children at risk owing to relatively low birth weight. Conclusion Normative differences in birth weight are a source of variability in children’s language, but postnatal socialization factors such as parenting may buffer this risk.