The behavioral phenotype of Williams syndrome (WS) is characterized by difficulties with establishment and maintenance of friendships despite high levels of interest in social interaction. Here, parents and teachers rated 84 children with WS ages 4-16 years using two commonly-used measures assessing aspects of social functioning: the Social Skills Rating System and the Social Responsiveness Scale. Mean prosocial functioning fell in the low average to average range, whereas social reciprocity was perceived to be an area of significant difficulty for many children. Concordance between parent and teacher ratings was high. Patterns of social functioning are discussed. Findings highlight the importance of parsing the construct of social skills to gain a nuanced understanding of the social phenotype in WS.