Autism spectrum disorder (ASD) is characterized by unusual social communication and interaction. These traits are often targets for intervention, particularly computer-based interventions (CBIs). We examined whether interactive behaviors in children with autism could be influenced by modifying the facial characteristics of computer avatars and how behavior toward avatars compared to that toward video. Participants spoke with a therapist over a modified videoconferencing system that permitted manipulation of her appearance (i.e., using cartoon or more realistic avatars versus video) and motion (i.e., exaggerating or damping facial movements). We measured the participants' speech, gaze, and gestures. In the first study, we found that the appearance complexity of the avatar did not significantly affect any social interaction behaviors. However, the results of the second study suggest that exaggerated facial motion can improve nonverbal social behaviors, such as gaze and gesture. These findings have implications for character design in CBIs for ASD.