Which is the more efficient mode of acqusition: Formal learning or informal acquiring? One cannot spend a second life to acquire a second language: There must be relatively quick acquisition medium and methodology, since a return to infancy is rather impractical, and, as a matter of fact, impossible given some maturational acquisitions. An L2 student already possesses some elements of L1, i.e. some language-learning experience, some knowledge of language architecture--however different that of L1 may be from that of L2. First-language acquisition begins with single-word utterances, to graduate to two-word sentences, and, eventually, to several-word sentences. Should an adult learn a new language this way? Semantic development goes hand-in-hand with grammatical development, precisely because content does not exist without form--and vice versa.
Only young, prepubescent learners, and then only those with good access to native-speaking peers and sufficiently rich and varied speaker input can--in the absence of formal grammar instruction, learn a foreign or second language with nativelike proficiency and accuracy. Postpubescent adolescents and adults need to pay some attention to the form of the target language. If they do not, they ultimately develop an incomplete and imperfect interlanguage that reflects learning problems such as negative transfer from the native language, simplification, overgeneralization, erroneous rule formation, and so forth (Celca-Murcia 406).
While comprehensible input is an essential part of the learning environment, it will not always be sufficient to bring about developmental changes or increased accuracy, even when learners are in supportive environments. We have seen evidence in our research that form-focused instruction can bring about changes in interlanguage and, furthermore, that there may be situations in which learners not only benefit from but require focused instruction to further their language acquisition (718).