PECS teaches communication through physical picture exchanges. The physical exchange is intentional — children learn that communication is a two-way social act with real outcomes.
Phase 1 — The physical exchange. Child picks up a single picture and gives it to a partner to receive a desired item. Physical prompt fades over trials.
Phase 2 — Distance and persistence. Child learns to seek out a partner across distance, travel to them, and complete the exchange.
Phase 3 — Picture discrimination. Child selects from multiple pictures to request the specific desired item.
Phase 4 — Sentence structure. Child builds a sentence strip: "I want ___". Introduces carrier phrases.
Phase 5 — Responsive requesting. Child responds to "What do you want?" with an appropriate picture sentence.
Phase 6 — Commenting. Child learns to comment ("I see ___", "I hear ___") — expanding to social communication.
Each phase must be mastered before moving to the next. Skipping phases undermines the system.