"From the moment a baby is born, they hear and respond to the spoken word. We bombard that infant with language for the first 12-18 months of their lives. During that time, we do not expect that they will utter a single understandable word.

Why then do we expect a child to spontaneously begin using an augmentative system from the first day they receive it? They too, need and deserve a period of learning from the models of others. This modeling can and should be done by parents, peers, siblings, professionals and others on a regular basis for an extended period of time. In this manner, the system becomes not only an expressive language tool but a receptive one as well."

and later in the article online:

"Remember: AAC Competency Takes Time!

Jane Korsten points out that the average 18 month old child has been exposed to 4,380 hours of oral language at a rate of 8 hours/day from birth. A child who has a communication system and receives speech/language therapy two times per week for 20-30 minutes sessions will reach this same amount of language exposure in 84 years."

From Considering AAC - Speech and Language, Common Myths & Resources on: http://atto.buffalo.edu/registered/ATBasics/Populations/aac/consider.php