There is an emerging supposition that autism spectrum disorder (ASD) originates from a failure to. According to this model, diminished sensitivity to social reward produces negative downstream consequences that coalesce into ASD symptomatology. That is, a child's failure to derive value from social interactions causes them to attend less to people and social events in their environment from which typically-developing (TD) children learn important skills. This failure to adequately engage with, and therefore learn from, the social environment contributes to the overt social impairments, atypical or restricted interests/behaviors, and communicative/cognitive delays that are characteristic of ASD. Unfortunately, the absence of a direct measure of social reward has limited the degree to which social reward theories of ASD can be empirically evaluated or advanced. The field has instead relied upon inferences drawn from indirect measures of other related constructs, such as impairments in social behaviors like joint attention or social responsiveness. Although useful, these measures are more likely capturing the consequences of deficits in social reward rather than directly measuring the primary impairment. The absence of a direct measure of social reward also has implications for the treatment of ASD: given that current measures assess only overt social impairments, most interventions to date have focused exclusively on addressing these observable symptoms rather than any underlying deficits in social reward processes. The proposed study will utilize the unique combination of expertise of our research group, which includes proficiency in behavioral economics, the treatment of ASD, and developmental neuroscience, to evaluate a direct measure that quantifies the degree to which children with ASD are sensitive to social reward. This project will build upon results of a previous pilot study, which demonstrated that an approach based on behavioral economics can measure sensitivity to social reward in terms of how hard an individual will work to produce an opportunity for social interaction. Results showed significant differences between TD children and those with ASD based on their work output for social interaction relative to work output for a preferred item. The proposed study will greatly expand on that previous work by including a group of participants with non- ASD developmental disabilities to control for the impact of intellectual disability on work output. The project will also evaluate the psychometric properties of the behavioral economic measure of sensitivity to social reward, including test-retest reliability and convergent/divergent validity. Finally, the behavioral economic measure will be used to evaluate whether a treatment developed by our research group to increase the rewarding properties of social interactions addresses the underlying deficit in sensitivity to social reward. Experience social interactions as rewarding