Children with autism spectrum disorder (ASD) display differences in multisensory function as quantified by several different measures. This study estimated the stability of variables derived from commonly used measures of multisensory function in school-aged children with ASD. Participants completed: a simultaneity judgment task for audiovisual speech, tasks designed to elicit the McGurk effect, listening-in-noise tasks, electroencephalographic recordings, and eye-tracking tasks. Results indicate the stability of indices derived from tasks tapping multisensory processing is variable. These findings have important implications for measurement in future research. Averaging scores across repeated observations will often be required to obtain acceptably stable estimates and, thus, to increase the likelihood of detecting effects of interest, as it relates to multisensory processing in children with ASD.