Impaired social communication and social reciprocity are the primary phenotypic distinctions between autism spectrum disorders (ASD) and other developmental disorders. We investigate quantitative conversational cues in child-psychologist interactions using acoustic-prosodic, turn-taking, and language features. Results indicate the conversational quality degraded for children with higher ASD severity, as the child exhibited difficulties conversing and the psychologist varied her speech and language strategies to engage the child. When interacting with children with increasing ASD severity, the psychologist exhibited higher prosodic variability, increased pausing, more speech, atypical voice quality, and less use of conventional conversational cue such as assents and non-fluencies. Children with increasing ASD severity spoke less, spoke slower, responded later, had more variable prosody, and used personal pronouns, affect language, and fillers less often. We also investigated the predictive power of features from interaction subtasks with varying social demands placed on the child. We found that acoustic prosodic and turn-taking features were more predictive during higher social demand tasks, and that the most predictive features vary with context of interaction. We also observed that psychologist language features may be robust to the amount of speech in a subtask, showing significance even when the child is participating in minimal-speech, low social-demand tasks.