Children with Autism Spectrum Disorder (ASD) are characterized by extreme deficits in social relatedness with same-age peers. The purpose of this descriptive study was to identify naturally occurring antecedent variables (i.e., setting events) in the classroom environments of children with ASD that promoted their engagement in peer-related social behaviors. Over a 12-week period, seven preschool-aged children were individually observed an average of 3.4-5.9 hours across the following classroom setting events: (a) contexts with varying peer group sizes, (b) contexts in which the adult or child directed the activities, and (c) contexts with varying levels of teacher engagement. Results based on a continuous, sequential behavioral coding system showed that for the majority of participants; small group sizes, child directed activities, and limited teacher engagement most influenced the occurrence of target children's social behaviors. Implications of this study to practice are addressed. (Contains 5 tables.)