Joint attention and imitation are thought to facilitate a developmental cascade of language and social communication skills. Delays in developing these skills may affect the quality of children's social interactions and subsequent language development. We examined how responding to joint attention and object imitation skills predicted rate of expressive and receptive communication growth rate in a heterogeneous sample of autistic children. Children's baseline skills in responding to joint attention uniquely predicted expressive, but not receptive, language growth rate over time, while object imitation did not significantly predict language growth rate over and above joint attention skills. Future research should examine the potential moderating roles of child age and developmental level in explaining associations between joint attention and object imitation and later language development.