http://www.anniesdandyblog.com/2009/03/york-university-speech.html
Anne Abbott, a nonspeaking person with cerebral palsy who uses a low-tech board to communicate , gave a speech to York University. She talks about how much we are at risk of having our communication took from us and gives advice for communicating with AAC users.
It was only when I started to venture out into the public on my own that I started having problems with communication. Some people were okay; they were patient enough to try to figure out what I was saying. However, there were others that just didn't get me. Right in front of me, I would hear them say things like, “Should she be alone?” I would point to words and letters on my communication board, and much to my annoyance I would hear people saying, “What do you think she wants?” From these kinds of experiences, I learned two things: one, to be patient with people who are actually trying to communicate with me; and two, if people don't understand what I'm all about, and they show me very little respect, I simply leave.
Unfortunately, there are times when a person like me can't just leave. People like me, who use Augmentative Alternative Communication, are frequently, and wrongly, silenced. Because of a lack of patience and understanding, or perhaps even a fear that they'll look ridiculous if they can't figure out what an AAC User is trying to say, people will often take away the person's Communication Device. This happens within the homes of AAC Users, where there is on-site attendant care. It can also happen if AAC Users are still living with their families, and unfortunately, it can often happen in hospitals or in nursing homes as well.
It takes patience and some intuition to start communicating with an AAC user. You have to be good at looking for cues in body language and facial expressions. This is not to say, however, that you're supposed to be a mind-reader. Make sure 100 percent that you got the message from the AAC user absolutely right before continuing the conversation. Use 'yes' and 'no' to confirm that you understood what they said. Also, some AAC users have different signs for 'yes' and 'no,' so make sure you know what they are beforehand.