The objective of the current study was to evaluate the patterns of longitudinal change in the language abilities of 28 children with autism during early and middle childhood. Results from fitting a series of multilevel models showed that children's rate of language growth was independently predicted by (a) children's responsiveness to others' bids for joint attention and (b) parents' responsiveness to their children's attention and activity during play. Both predictive relations could not be explained by initial variation in global developmental characteristics, such as IQ, mental age, or language abilities. These findings support a social-pragmatic view on language acquisition, which emphasizes the collaborative process through which children and their parents negotiate shared meaning.