More research suggesting that the teaching of grammar explicitly is not especially useful, and that the best way to master a second language is through massive comprehensible input.
Language and literacy can be”acquired” or “learned.” “Acquisition” occurs subconsciously: While it is happening, you are not aware it is happening, and after it has happemed, the knowledge is represented subconsiously in your brain. In contrast, “learning” is conscious; it is “knowing about” the language. When we talk about “rules” and “grammar” we are usually talking about “Learning.”
Acquired competence plays a much larger role in language use than learned competence does. Acquired competence provides our fluency and nearly all of our accuracy when we speak or write in a second language. Learned competence makes only a small contribution to our grammatical accuracy, and only when stringent conditions are met: We must consciously know the rule, which is daunting considering the complexity of the grammar of any language, we must have time to apply the rule, which is not usually available in conversation, and we must be thinking about correctness, or focussed on form.
This is not to say that grammar teaching is bad and must be forbidden: The point is that it is limited: Only a small part of the grammatical system of any language can be consciously learned, it takes time and effort to retrieve grammatical rules from our memory and apply them, and this can only happen when we are thinking about formal correctness. These severe conditions are met on grammar tests, and it is here where see clear evidence of the use of consciously learned rules (Krashen, 1981). Consciously learned rules are also of some help in editing, the final stage of the composing process.