8 - Language learning and language acquisition processes
The picture above summarizes the language learning processes in a simplified way. One cannot learn a language if there is no input. Explicit or implicit language input allows the learner to develop hypotheses. Students need to have lots and lots of opportunities for language production (to test their hypotheses) on which they get feedback to improve their production. These are evidence-based conditions for a strong language acquisition approach.
Also, language acquisition is, of course, not obtained in a linear fashion. It is a whimsical, unpredictable and individually different process.