Sibling-mediated interventions (SMI) have the potential to increase social communication, play, and interpersonal skills for children on the autism spectrum. However, less is known about effective practices for training siblings to be intervention mediators. Existing SMI systematic reviews and meta-analyses have focused on the effects of SMIs for children on the autism spectrum. The purpose of this meta-analytic review was to (a) examine the methodological quality of existing single-case experimental design SMI studies based on What Works Clearinghouse standards; and (b) calculate omnibus effects for participants with autism and their siblings. Nineteen studies were located which met standards with or without reservations. Omnibus effect sizes were low for children with autism and moderate for neurotypical siblings.