Behaviourists propose that a child’s environment is the most important factor in first language acquisition, and if a child is exposed to ‘rich language,’ then ‘good habit formation,’ and proper language development will occur. It is possible that first language acquisition includes speech imitation, but:
Children do not imitate everything they hear; they appear to be very selective and only reproduce unassimilated language chunks. Therefore, their replications seem to be controlled by an internal language-monitoring process.
Children learn the basic rules of language at around the age of five; the behaviourist theory cannot account for the speed that first language is acquired.
Children say things that are not adult imitations; in particular they use inflectional overgeneralisations such as ‘goed,’ ‘putted,’ ‘mouses,’ and ‘sheeps.’
Children produce language structures that do not exist; you often hear, “Where I am?” instead of “Where am I?”
Children that acquire language from habit formation seem to memorize certain structures prematurely. These phrases become lodged in their minds as unassimilated chunks of information that they cannot incorporate into their own verbal expressions.
Children produce many more sound-combinations than they hear, and understand many more than they can produce.
Children are exposed to language performance and not to language competence. Often they are exposed to “debilitated” language, yet, they manage to extract the language rules from these utterances and speak correctly.