The Picture Exchange (PE) is  a low-tech aided system of AAC.

Throughout PE, the individual learns to exchange cards with pictures on them for access to items, activities or attention. This system encourages the individual to communicate their needs to their communication partners in a way that is accessible when they have no or very little verbal language. The purpose of this system is to slowly develop the individual's confidence and desire to communicate their needs and engage in social situations. 

Picture Exchange Communication System (PECS) is a type of PE that has a set protocol of phases. PECS is delivered in six phases, each phase builds on top of the new communication skills they have developed in previous phases.  

Phase 1: Physical Exchange/How to communicate

Individuals learn to exchange a picture for an object that is desirable for them. For example; a toy, a snack or a beverage.
In this phase (unless there have been modifications made to accommodate the individual's physical ability) they must pick-up, hand over and release the picture card that shows the desired option to the communication partner, who will then give them the item.  

Phase 2: Distance and Perspective

The individual is taught to move to use the AAC system whenever they desire an item in a variety of different settings. This shows that they understand the purpose and they will persist in using the AAC system in different contexts. 

Phase 3: Picture/Figure Discrimination

The individual is presented with more than one card at a time and are taught to make active choices between them. They are taught to choose cards that are relevant and appropriate to the situation and to the current communication partner. 

Phase 4: Sentence Structure

The individual is taught to create simple sentences by using sentence starter strips.
For example, they might select or tap on a strip that  says  "I want",  and then select/tap a picture of the desired item. (e.g.. "I want" followed by "book").

Phase 5: Responding to a requesting question

The individual is taught and encouraged to respond to questions like "What do you want?" or "What else do you want?" by using the cards to indicate their desires. 

Phase 6:  Commenting

The individual is taught to answer objectively more complicated questions (eg. "What is this?" or "What show are you watching?" using the cards. They are also encouraged to use the cards to comment independently on the situations or events that are happening around them .