Shaping

Shaping is how you teach behaviours that a learner can't yet perform at all. You start by reinforcing whatever they can do that resembles the target, then gradually raise the criterion as they improve.

Teaching a non-verbal learner to make sounds starts by reinforcing any vocalisation. Then only louder ones. Then ones that resemble the target phoneme. Then the full word approximation. You're sculpting the behaviour by controlling what gets reinforced at each step.

The art of shaping is knowing when to raise the criterion. Move too fast and the learner stops contacting reinforcement and the behaviour falls apart. Move too slow and you get stuck at an intermediate approximation that becomes its own habit. Good shaping requires close observation and a willingness to drop back a step when the data say to.