You have to wait
Your AAC user needs you to slow down and give them time to communicate. Exactly how much wait time is required depends on your unique user, but somewhere between 15-60 seconds can be an excellent place to start.
The more complex your AAC user's needs (language processing, motor planning), the more time they may need.
Give them time to:
• consider their thoughts and perspective
• process what was said
• shift attention to and from other thoughts or stimuli in the environment
• think if it's worth the effort to respond
• consider where the needed language is in the AAC system
• formulate a response in their head
• select language on their AAC and play the message
• organize their body to access the AAC system