Background: Down syndrome (DS) has been the focus of much cognitive and developmental research; however, there is a gap in knowledge regarding sustained attention, particularly across different sensory domains. This research examined the hypothesis that children with DS would demonstrate superior visual rather than auditory performance on a sustained attention task and that this modality difference would not be seen in children with non-specific intellectual disability (NSID). Materials and Methods: Eleven children with DS and 16 children with NSID were compared on two versions of the sustained attention to response test (SART), varying only in presentation modality (visual or auditory). Errors of commission (failure to withhold response to target) and errors of omission (failure to respond to non-target distractors) were recorded. Results: Significant group differences were found in the visual modality and mental age was also found to effect error rates in the visual condition. No effect of group or mental age was observed in the auditory SART. Conclusions: Results suggest that, for individuals with DS, presentation of education material in a visual medium may facilitate sustained attention and thus learning. Further research using tools such as the SART to explore modality differences in sustained attention and additional cognitive domains is recommended.