BackgroundSustained attention (SA) is important to task performance and development of higher functions. It emerges as a separable component of attention during preschool and shows incremental improvements during this stage of development. AimsThe current study investigated if auditory and visual SA match developmental level or are particular challenges for youth with DS. Further, we sought to determine if there were modality effects in SA that could predict those seen in short-term memory (STM). Methods and proceduresWe compared youth with DS to typically developing youth matched for nonverbal mental age and receptive vocabulary. Groups completed auditory and visual sustained attention to response tests (SARTs) and STM tasks. Outcomes and resultsResults indicated groups performed similarly on both SARTs, even over varying cognitive ability. Further, within groups participants performed similarly on auditory and visual SARTs, thus SA could not predict modality effects in STM. However, SA did generally predict a significant portion of unique variance in groups’ STM. Conclusions and implicationsUltimately, results suggested both auditory and visual SA match developmental level in DS. Further, SA generally predicts STM, though SA does not necessarily predict the pattern of poor auditory relative to visual STM characteristic of DS.