Background: To develop effective education strategies, a detailed knowledge of the working memory profile in Down syndrome (DS) and autism with intellectual disability (ID) is required. Materials and Methods: Fifteen adolescents with DS, 11 boys with autism and ID, and 12 boys with nonspecific ID (NSID) were compared on 2 versions of a novel working memory task that varied only in modality of presentation (visual or auditory). Results: The groups with DS and with autism and ID demonstrated significantly poorer working memory performances than the group with NSID. No predictors of working memory performance were found. Conclusions: Recommendations to support the working memory difficulties of the groups with DS and autism and ID in the classroom include reducing the amount of information to be processed at a time, as well as providing visual or verbal (as appropriate) prompts and cues to reduce the need to hold information in working memory.