This study examined the effectiveness of an instructional program designed to teach grammar skills to individuals who communicated via augmentative and alternative communication (AAC). A single-subject, multiple-probe, across-behaviors design was used to measure the effect of the instructional program on the acquisition and maintenance of the skills learned. Two adults with cerebral palsy participated in the study. The instructional program was used to teach two grammatical forms to each participant. Word order in adjective phrases and inversion of the auxiliary do in wh- questions was targeted for one participant; use of possessive pronouns and the inclusion of to when using infinitives as modal verbs was targeted for the second participant. The instructional program was shown to be effective. Both participants learned to produce the grammatical forms taught. One participant maintained these skills for at least 2 months after the completion of instruction; the other participant required additional instruction in order to maintain the skills learned. Although based on a small sample, the results suggest that intervention can help individuals who use AAC improve their grammar skills. Limitations of the study are discussed, along with directions for future research.