Baby imitating sounds. Beginning vocal imitation: ABA example
Channel: Good Behavior Beginnings
Date: 2013-08-03

When beginning to teach vocal imitation (in order to teach language), you start by reinforcing approximations or good attempts at making the sound. 

In this video, the provider is praising any sound made by the learner after given the instruction to "say ah". In the future, the provider will only reinforce those sounds that more closely resemble the modeled sound. Eventually, the provider will only reinforce accurate imitations of the modeled sound.