By Matt Harrington, BCBA · Behaviorist Book Club · Research-backed answers for behavior analysts
Phase I teaches the physical exchange: handing a single picture to a communicative partner in exchange for a desired item. Phase II extends the exchange across increasing distance between the learner and the communicative partner. Phase III teaches picture discrimination — choosing the correct picture from an array when multiple options are present. Phase IV introduces the sentence strip and 'I want' card, teaching multi-word requests. Phase V teaches responding to the question 'What do you want?' by constructing a sentence strip. Phase VI adds commenting, extending the communicative function beyond manding to include tacting and intraverbal responses.
The two-instructor format separates the physical prompter from the communicative partner to prevent prompt dependency on the partner's physical presence. The communicative partner holds the preferred item and waits for the exchange without speaking or physically guiding the learner. The prompter, positioned behind the learner, uses hand-over-hand guidance to physically assist the exchange. This arrangement ensures the social contingency — receiving the item in exchange for the picture — is clear and unconditional, while the physical prompting is delivered by a person who is not the reinforcement source, making fading to independence more straightforward.
Picture selection should begin with a preference assessment identifying items and activities that currently function as reinforcers for the learner. Pictures should represent high-preference items that the learner is motivated to request under naturalistic motivating conditions. The visual style — photographs, line drawings, or symbol-based icons — should be selected based on the learner's visual discrimination ability. Pictures should be culturally relevant and reflect the learner's actual environment and preferred items. As the PECS program advances through phases, the picture inventory expands to include a broader vocabulary across motivating categories.
The standard PECS error correction procedure for Phase III uses a four-step format: prevent access to the item following the incorrect exchange; redirect the learner's attention briefly away from the materials; prompt the correct exchange using the least intrusive effective prompt; and then reinforce the correct exchange with access to the requested item. Error corrections should be delivered with neutral affect and without verbal commentary about the error. Consistent implementation of this procedure across all trainers prevents the learner from learning to discriminate between instructors who do and do not implement corrections.
A consistent finding in the PECS literature is that a subset of learners who receive PECS instruction show increases in spontaneous speech, with some studies reporting that speech development accelerates rather than being impeded by the introduction of a picture-based system. This finding challenges the concern that using AAC will reduce motivation to develop speech. The mechanism is not fully understood, but the mand training embedded in PECS — teaching functional requesting under naturalistic motivating conditions — may support the development of vocal mands in learners with some emerging vocal behavior. BCBAs should present this research to families concerned about the relationship between PECS and speech.
Generalization should be systematically programmed rather than assumed to occur naturally. Strategies include: training with multiple communicative partners from the earliest phases, conducting PECS sessions in multiple settings (clinic, home, school, community), varying the picture stimuli across different visual formats, and building in regular generalization probes with novel partners and in novel settings. Caregiver training is essential — parents and teachers who implement PECS consistently outside of therapy sessions create the naturalistic generalization conditions that support durable functional communication.
The decision to transition from PECS to a speech-generating device should be individualized and data-based. Indicators supporting transition include: mastery through Phase IV or beyond, demonstrated ability to discriminate among multiple picture symbols, emerging vocal behavior suggesting AAC-supported speech development, caregiver preference for high-tech AAC, and functional access to a device. An SLP should be involved in the AAC evaluation and device selection process. PECS and a speech-generating device are not mutually exclusive — some learners use both in different contexts — so the decision is not always either-or.
PECS training for RBTs should follow a BST format: provide verbal instruction on the rationale and procedure, model each instructor role (communicative partner and physical prompter), give the supervisee practice opportunities in structured role-plays, and provide specific performance feedback. Training should cover Phase I physical guidance and fading, Phase III error correction procedure, and the sentence strip protocol in Phase IV at minimum. Directly observe RBTs implementing PECS with learners before approving independent implementation, using a fidelity checklist to provide specific, behavior-anchored feedback.
PECS targets the mand relation as defined in Skinner's verbal behavior analysis — a verbal operant controlled by a motivating operation and reinforced by access to the specified item or event. By beginning with mand training, PECS ensures that the learner's first communicative acts are directly reinforced by the natural consequence of the communication (receiving the desired item), creating strong motivational conditions for communication. This is in contrast to labeling or imitation-based communication training, which may not produce direct reinforcement for the learner. As PECS advances to Phase VI, commenting (tacting) is also addressed.
Code 2.01 (scientifically supported interventions) supports the use of PECS given its evidence base. Code 2.09 (least intrusive procedures) is relevant to the physical guidance used in Phase I and requires that guidance is faded systematically. Code 1.01 (beneficence) obligates BCBAs to advocate for functional communication programming for non-vocal learners. Code 2.03 (informed consent) requires caregivers to understand and consent to physical guidance procedures. Code 4.05 (supervision) requires that RBTs are trained and observed before implementing PECS independently.
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All behavior-analytic intervention is individualized. The information on this page is for educational purposes and does not constitute clinical advice. Treatment decisions should be informed by the best available published research, individualized assessment, and obtained with the informed consent of the client or their legal guardian. Behavior analysts are responsible for practicing within the boundaries of their competence and adhering to the BACB Ethics Code for Behavior Analysts.