A training technique in which a complex behaviour is built up by reinforcing successive small steps that progressively resemble the final goal. Each step is reinforced until it is reliable, then the criterion is raised and only the next-closer approximation is reinforced.

Teaching a horse to self-load onto a float by reinforcing each forward movement, then each step toward the ramp, then each foot on the ramp, then each foot inside, then standing calmly inside with the bar closed, is shaping. The same approach is used to train medical husbandry behaviours in zoo animals (presenting a paw for a blood draw, opening the mouth for an oral exam), retrieves and recalls in dogs, vocalisations in parrots, and a wide range of behaviours across species in modern applied animal training.

Shaping is one of the most useful techniques in the trainer’s toolkit because it allows behaviours to be taught that the animal would never spontaneously offer in their full form. By reinforcing the smallest available step toward the goal, the trainer can build complex behaviours one increment at a time.

The key skill in shaping is choosing the right size of step for the individual learner. Steps that are too small produce slow progress and can frustrate the animal; steps that are too large produce failure and lost reinforcement opportunities. Skilled shaping involves continuous adjustment of the criterion based on what the animal is offering. The technique is sometimes called successive approximation when the small-step mechanism is being emphasised.

Shaping is generally taught and applied using positive reinforcement, often with a bridging signal such as a clicker, but the principle works with any reinforcer.