Atypical prosody, often reported in children with Autism Spectrum Disorders, is described by a range of qualitative terms that reflect the eccentricities and variability among persons in the spectrum. We investigate various wordand phonetic-level features from spontaneous speech that may quantify the cues reflecting prosody. Furthermore, we introduce the importance of jointly modeling the psychologist's vocal behavior in this dyadic interaction. We demonstrate that acoustic-prosodic features of both participants correlate with the children's rated autism severity. For increasing perceived atypicality, we find children's prosodic features that suggest 'monotonic' speech, variable volume, atypical voice quality, and slower rate of speech. Additionally, we find the psychologist's features inform their perception of a child's atypical behavior– e.g., the psychologist's pitch slope and jitter are increasingly variable and their speech rate generally decreases.