Purpose: In this study, we investigated the efficacy of a least-to-most (LTM) prompting procedure (Ault & Griffen, 2013; MacDuff, Krantz, & McClannahan, 2001; Neitzel & Wolery, 2009) for increasing use of multisymbol messages in school-age children with autism spectrum disorder (ASD) who use augmentative and alternative communication (AAC) during a storybook reading activity. Method: In the study, we used a single-subject, multiple-probe research design across participants (Kazdin, 1982) with 6 children (ages 8–12) with ASD and who used AAC systems for communication. There were 4 phases in this investigation: (a) baseline, (b) intervention, (c) generalization, and (d) maintenance. Results: All participants exhibited a positive increase in multisymbol message production almost immediately upon introduction of the LTM prompting procedure. Conclusions: The results of the investigation contribute important information on the efficacy of the LTM prompting procedure for teaching use of multisymbol messages to school-age children with ASD who use AAC.