Shaping With Successive Approximations

Foundations of Shaping and the Role of the RBT

In applied behavior analysis, shaping is defined as the differential reinforcement of successive approximations toward a terminal behavior. A terminal behavior represents the final target response desired at the conclusion of a shaping program. For example, if a learner is working toward speaking full words, the terminal behavior might be the spoken word 'ball.' Before any teaching begins, the terminal behavior must be defined in objective, observable, and measurable terms in the client's skill acquisition plan. This precision ensures that anyone reading the plan knows exactly what the finished skill looks like.

Developing this clinical plan is the responsibility of the supervising Board Certified Behavior Analyst (BCBA), or a Board Certified Assistant Behavior Analyst (BCaBA) working under BCBA supervision. The supervisor designs the shaping program, defines the terminal behavior, and outlines each intermediate step. As a Registered Behavior Technician (RBT), your primary role is to implement the written protocol with fidelity and collect accurate data. RBTs do not invent new approximation steps, change clinical goals, or modify behavior plans independently. Instead, RBTs carry out the prescribed protocol during direct sessions and communicate closely with the supervisor.

Shaping is especially useful when a learner does not yet perform the terminal behavior reliably, but can perform an initial response that can be gradually changed toward that target. A shaping plan starts with an approximation the learner can already perform or that can be reliably evoked, for example with a prompt specified in the plan. The starting response should be achievable often enough for the learner to contact reinforcement, as specified in the supervisor's plan. From this starting point, the learner works through successive approximations, which are intermediate behavioral steps that progressively resemble the terminal target response. These steps must be achievable and gradual enough for the learner to contact reinforcement regularly throughout the learning process.

Before beginning each session, the RBT should review the exact operational definition of the target approximation currently assigned in the plan. Reviewing these definitions helps you reinforce responses that meet the current written criterion, following the plan's reinforcement instructions. When an RBT reinforces an approximation that falls short of the current written criterion, it can inadvertently reinforce lower-level responding and delay learning. Conversely, failing to deliver reinforcement when a client performs the correct approximation can weaken the behavior. Clear understanding and consistent implementation across all RBTs on the clinical team are critical for a shaping program to succeed.