There is no agreement on a “complete” theory of second language acquisition yet.
Each theoretical framework has a different focus and its limitations.
Behaviorism: emphasizing stimuli and responses, but ignoring the mental processes that are involved in learning.
Innatism: innate LAD, based on intuitions
Information processing and connectionism: involving controlled laboratory experiments where human learning is similar to computer processing.
Interactionist position: modification of interaction promotes language acquisition and development.