Cross-informant ratings of are considered gold standard for child behavioral assessment. To date, little work has examined informant ratings of adaptive functioning for youth with autism spectrum disorder (ASD). In a large, diverse sample of youth with ASD, this study evaluated parent-teacher concordance of ratings of adaptive functioning and ASD-specific symptomatology across time. The impact of child clinical characteristics on concordance was also examined. Participants included 246 children, their caregivers and teachers. Parent-teacher concordance was variable but generally consistent across time. Concordance was significantly impacted by autism severity and child cognitive abilities. Findings inform the broader concordance literature and support the need to consider child clinical factors when assessing child functioning in samples of children with ASD. [At time of submission to ERIC this article was in press with "Journal of Autism and Developmental Disorders."]