If you are a parent of a non-verbal child on the spectrum, you will have agonized over this topic. These children need a way to communicate and in particular to communicate their needs. Without a functional communication system, the child will use other means of communication, like leading an adult to what they want, or crying, screaming, and self-abuse.
The most common system introduced to children is the Picture Exchange Communication System (PECS). The goal of this system is to make a child an initiator (not just a responder) of communication and to understand its usefulness through exchange of pictures for desired items. Later, children can make comments and have simple communication exchanges with PECS. This is the system Alanna uses. There are six phases of PECS; Alanna has remained in phase three for months. Currently she is able to go to her communication book, choose what she wants (or choose something representing a label if we ask her what something is) and bring it to us. If it is a request she does it spontaneously without help and she brings it because she is internally motivated to get something. We have not gone to phase IV because that phase introduces sentence structure, and we had, to this point, been making good progress on speech. The concern from our psychologist was that Alanna could just start saying "I want" instead of the actual items, which she was at that point. However, her vocals have really decreased. Hours of mand training for good clear approximations are now met with silence or throaty "guh guh" sounds. So now the question... continue with mand training with this much intensity or dial it back and introduce more complex PECS to allow Alanna to speak in sentences and comment?
Verbal behaviourists like Dr. Mark Sundburg, Dr. James Partington, or Dr. Vince Carbone are fairly persistent in their view that non-verbal children should be taught sign language. Don't get me wrong; we use a verbal behaviour type therapy approach. However, sign language is not always suitable... Alanna, for example, has a lot of trouble with imitation in general. She is improving, but her language acquisition is much faster with PECS. There is also the problem of usability - most people are not going to understand sign, especially if they are approximations. However, a sentence of pictures is clear to almost anyone.
There are problems with PECS, though. Eventually she will have too many and we will have to switch to a voice system if she is not vocalizing or picking up some sign. To me, PECS seems more functional for long term use, but sign language seems better for learning how to talk. Obviously, we want her to talk!
Here's hoping for some clear direction...