•We investigated the accuracy and efficacy of primary caregivers’ AAC intervention implementation with one adult with ASD.•Participants were four primary caregivers and one adult with ASD.•We implemented a single-case multiple probe design.•Results indicated that caregiver participants rapidly met the mastery criteria.•The participant with ASD used the AAC app independently more often during intervention phases than during baseline. Many researchers have investigated the effectiveness of augmentative and alternative communication (AAC) systems on improving communication skills of children with autism spectrum disorder (ASD) and communication complex needs (CCN); however, few studies included adults with ASD. Also, there is a lack of research on primary caregiver implemented interventions with high treatment fidelity although primary caregiver-implemented interventions have been used effectively with adults with ASD and their families. This study investigated the accuracy of primary caregivers’ implementation of a tablet-computer based AAC system while they were providing instruction to an adult with ASD. Also, independent use of AAC system of the participant was examined. We implemented a multiple probe design across three instructional coaching steps to examine the accuracy of the caregivers’ AAC implementation. One adult with autism and CCN and his four primary caregivers participated in this study, twice a week for seven weeks. Both visual and statistical analyses were utilized. Results indicated that, with instructional coaching, all of the caregivers were able to implement the procedures of the AAC mode with the participant accurately, as demonstrated via visual inspection and statistical analyses. Nevertheless, there was little improvement in the participant's independent use of the AAC mode. Limitations and suggestions for future researchers are discussed.