At what age should second language instruction begin?
After reading the critical period studies, it is tempting to say, 'I didn't start studying a second language in childhood, so what's the point of trying?' or, 'If second language teaching programs are to succeed, they had better begin with very young children'. However, we know that even if native-like mastery of a second language is usually not possible for learners who begin learning later in life, experience and research both show that older learners are able to attain high levels of proficiency in their second language. Furthermore, it is essential to think carefully about the goals of an instructional program and the context in which it occurs before we jump to conclusions about the necessity-or even the desirability-of the earliest possible start.
The role of the critical period in second language acquisition is still a much debated topic. For every researcher who holds that there are maturational constraints on language acquisition, there is another who considers that the age factor cannot be separated from factors such as motivation, social identity, and the conditions for learning. They argue that older learners may well speak with an accent because they want to continue being identified with their first language cultural group. And adults rarely get access to the same quantity and quality of language input that children receive in play settings.

Many people conclude on the basis of studies such as those by Patkowski, and Newport and Johnson that it is better to begin second language instruction as early as possible. Yet it is very important to bear in mind the context of these studies. They deal with the highest possible level of second language skills, the level at which a second language speaker is indistinguishable from a native speaker. But achieving a native-like mastery of the second language is not a goal for all second language learning, in all contexts. When the objective of second language learning is native-like mastery of the target language, it is usually desirable for the learner to be completely surrounded by the language as early as possible. However, in the case of children from minority language backgrounds or homes where language, literacy, and education are not well-developed, early intensive exposure to the second language may entail the loss or incomplete development of the child's first language. This leads to so-called subtractive bilingualism, where one language is lost before another is fully developed. Subtractive bilingualism may, in turn, lead to academic and personal problems. For these children, programs promoting the development of their first language at home and at school can help to prevent some of these problems. Such programs allow children to continue to use their stronger first language while they learn the second language. This encouragement of the first language can have positive effects on the children's self esteem, on their relationships with their parents, on their early cognitive development, and somewhat paradoxically, on their eventual mastery of the second language.