What is the PRIMARY distinction between Phase 3 and Phase 4 of PECS?

The primary distinction between Phase 3 and Phase 4 of the Picture Exchange Communication System (PECS) lies in the shift from requesting single items to requesting *sentences* and demonstrating an understanding that pictures represent *spoken words*. PECS is a structured intervention designed to teach individuals with autism or other communication challenges to initiate communication by exchanging pictures for desired items.

Phase 1 focuses on establishing the foundation: teaching the individual to exchange a single picture for a desired tangible item. For example, a child might exchange a picture of a cookie for an actual cookie. Phase 2 builds on this by expanding the repertoire of pictures and introducing the concept of asking for multiple items sequentially. The child learns to hand over one picture, then another, to request several items. Phase 3, however, introduces *sentence structure*. This phase requires the individual to spontaneously request items by combining two pictures, creating a simple sentence. A key element of Phase 3 is the introduction of the “I want” card. The individual must present the “I want” card *before* presenting the picture of the desired item. For instance, the child would hand over the “I want” card, then the picture of juice, to communicate “I want juice.” This demonstrates an understanding that the picture represents a spoken word and that a specific sequence of pictures can convey a more complex message. Crucially, in Phase 3, the communication partner (e.g., therapist, parent) *models* the sentence structure, prompting the child to imitate.

Phase 4 marks a significant advancement. Here, the individual must *spontaneously* use two-picture sentences without prompting. The communication partner no longer models the sentence. The child independently initiates the request using the “I want” card and the picture of the desired item. This phase assesses whether the individual has generalized the sentence structure learned in Phase 3 and can use it independently in different settings. The focus shifts from imitation to independent communication. If the individual consistently and spontaneously uses two-picture sentences, they are ready to move on to Phase 5, which introduces more complex sentence structures and conversational skills.