The purpose of this study was to examine how total duration of social play of preschool children with disabilities varied as a function of both chronological and developmental age of their social partners. Fifty-five 33- to 60-month-old children with mild to moderate developmental delays were observed in dyadic play situations with four different partners. Partners ranged from same age as the focal child to 23 months difference in age, and ranged in developmental status from typical to moderate delay. Results indicated that the influence of partner's developmental age on social play was different depending on the developmental age of the focal child. This interaction effect suggests that advantages accrued to preschoolers with disabilities from mixed-aged play groupings depend on the child?s developmental age and those of available social partners.