Research shows that AAC does not impede the development of speech and language skills. It actually indicates that AAC facilitates spoken language by increasing interaction, improving language skills, and/or providing a voice output model for speech. Additionally, research shows that children who are not able to communicate effectively by some means are at great risk for cognitive, social, emotional, and behavioral problems. The purpose of AAC is to provide a functional communication system, which may be used short or long term.
For additional information, please see this resource: AAC: An Introduction
Romski, M.A., Sevcik., R.A., Reumann, R., & Pate, J.L. (1989). Youngsters with moderate or severe retardation and severe spoken language impairments. I: Extant communication patterns. Journal of Speech and Hearing Disorders, 54, 366-373.
Bodine, C. & Beukelman, D.R. (1991). Prediction of future speech performance among potential users of AAC systems: A survey. Augmentative and Alternative Communication, 7 (1), 100-111.
Millar, D., Light, J., and Schlosser, R.(1999). The impact of augmentative and alternative communication (AAC) on natural speech development: a meta-analysis. Poster session presented at the American Speech-Language-Hearing Association Annual Conference, San Francisco, CA