When setting up an AAC device or app, it can be very difficult to determine a starting vocabulary. While I am an advocate for core word vocabulary, I strongly believe in starting with a small amount of vocabulary and then quickly increasing.
During this beginning phase of using a small vocabulary set, the AAC user will only be able to tell us what we have anticipated; howevever, it is important the user succeed during these early days so they understand the power and importance of communication. It is also vital that parents, teachers, and family members have buy-in, so we must make the launch of AAC as easy and successful as possible.
Here is a video with more information on selecting early vocabulary for AAC: