We examined the relations of verbal ability and self-regulation in preschool to emotion knowledge in first grade, and concurrent relations between emotion knowledge and indexes of social functioning in 143 children from low-income families. After controlling for children's verbal ability in preschool, teacher reports of attentional control and caregiver reports of behavioral control in preschool predicted children's emotion expression knowledge and emotion situation knowledge 2 years later. After controlling for verbal ability and attentional and behavioral control, children's emotion knowledge predicted concurrent teacher-reported social problems and social withdrawal. Results suggest that low levels of emotion knowledge co-occur with many important aspects of children's early social adaptation.