There is a common myth about second language acquisition that by six or seven years old, it is too late to acquire a language fully. This argument is based on the “critical period hypothesis.” I admit that linguistics research is not easily accessible and linguists are notoriously poor at disseminating their findings to the public. Because of that, I can’t blame anybody for believing that older children can’t learn a second language with perfect fluency. Even researchers and academics have stated this claim to the wider public. (See this popular Ted talk). However, this is a very simplistic view of language acquisition, especially given the competing viewpoints on the topic.
It is generally believed that learning a language earlier, as a young child, is better but little reliable scientific evidence exists to prove this. There are even studies showing the opposite (e.g., DeKeyser’s study). Most studies focusing on these issues do indeed mention the “critical period hypothesis,” known as CPH. In terms of language (as CPH applies to many different developmental processes like hearing and vision), the critical period is when language must be acquired to ensure the development of native competence. After this period is over, the ability to learn a language is affected.
CPH for language was developed in the late sixties by Lenneberg. He claimed that a child’s brain plasticity (or flexibility) makes learning a language (among other things) easier. This plasticity starts disappearing by age seven. By age 12, it is too late to put it bluntly. The brain has lost its plasticity and learning a language is more difficult. This is true for first, second or third language learning. According to CPH, in extreme cases of deprivation, such as feral children, a child who has not been exposed to language by age seven will never learn to use language appropriately.
The pressing question for many researchers is whether there is an age limit for language acquisition to ensure native fluency. Researchers in the field are also asking if there is indeed a critical period for language acquisition. Within the very large body of scientific literature on the subject, studies point to differences in the way the language is processed and acquired depending on the learner’s age.
Research comparing the acquisition of a second language in natural settings (i.e., not in a classroom) has consistently shown that young children are initially slower than teenagers or young adults but these younger students catch up and eventually overtake older learners (Snow and Hoefnagel-Hohle, 1978). Older learners, on the other hand, may benefit from better metalinguistic processing, which is the ability to think about the language as a process.
The balance of evidence for and against CPH continues to puzzle researchers and inspire lively debate. The current discussion around CPH deals with the alleged age limit of seven as the cut-off point, which is not clear-cut. Recent studies are showing that the critical period may influence different aspects of language differently. Vocabulary is the least affected area of language. We can indeed learn new words in a new language at any age, although it doesn’t mean we can put them together appropriately. Older learners are as good as younger ones when it comes to acquiring new words. Pronunciation, on the other hand, is impacted the most by this critical period. Younger learners are generally better at pronunciation. I’m sure you know of young children who sound just like native speakers and older learners who, even after years of learning a language, retain accents. So, there may actually be several cut-off points rather than one. Some of these thresholds happen very early (some believe around three or four years old) and others very late.
The evidence to date thus remains patchy and inconclusive. No systematic comparison of the acquisition process at different ages in similar contexts has been conducted. Earlier may be better for some aspects of language, but younger learners also learn slower initially. Studies have also demonstrated the ability to attain full proficiency and be very successful as a language learner past these so-called thresholds. This is what makes this issue so perplexing for researchers.
Note: This article is about learning a second language after the ages of three or four. Learning two or more languages before that age is a whole different concept in terms of linguistic research (multilingualism).
Lenneberg, E.H. (1967). Biological Foundations of Language. Wiley.
Olson, L, and Samuels, S.J. (1973). The relationship between age and accuracy of foreign language pronunciation. Journal of Educational Research, 66, 26-267.
DeKeyser, R. (2000). The robustness of critical period effects in second language acquisition, SSLA, 22, 499–533.
Snow, C.E. & Hoefnagel-Hohle, M. (1978). Critical period for language acquisition: Evidence from second language learning. Child Development, 49, 1263-1279.
Bialystok, E. and Hakuta, K., (1994). In Other Words: The Science and Psychology of Second- Language Acquisition. New York: Basic Books.