Scientists have long posited that there is a “critical period” for language learning, but new research suggests that the time frame stretches on much longer than previously thought.
The study, from the Massachusetts Institute of Technology, suggests that children remain skilled at learning the grammar of English up to the age of 17 or 18, the time at which many students graduate from high school.
The finding injects new evidence for the decades-long debate over the “critical period” that had centered on whether the decline in language-learning skills begins at age 5 or at the onset of puberty.
The research could have implications for K-12 schools, where the number of English-as-a-second-language speakers is on the rise, but the quality of education those students receive has faced increased scrutiny. The findings could be especially relevant for the education of newcomer immigrant and refugee English-learners who arrive in the United States as middle and high school students.
"[The work] should raise teachers’ sense of self-efficacy ... that they do have a tremendous impact on second-language learners who are in their secondary school years,” said Shannon Daniel, a senior lecturer at Vanderbilt University’s Peabody College of Education whose work focuses on improving English-language-learner-education in U.S. schools.
The same MIT study also found that it is difficult for people to achieve proficiency in English similar to that of a native speaker unless they start learning a language much earlier, by the age of 10. People who start learning a language between the ages of 10 and 18 will still learn quickly, but since they have a shorter window before their learning ability declines, they’re less likely to reach the proficiency of native speakers, the researchers found.
“It takes work on the part of the parents, but, as far as the child’s concerned, it’s quite easy to become bilingual,” Joshua Hartshorne, an assistant professor of psychology at Boston College, who conducted the study as a postdoctoral scholar at MIT. “That’s when you’re best at learning languages. It’s not really something that you can make up later.”
What Is Bilingualism?
A March 2017 study from the National Academies of Sciences, Engineering, and Medicine detailed how underresourced schools and underprepared educators hinder efforts to help students learn and master English. The report’s authors contend that teacher- and principal-preparation programs must adapt their curricula and training to ensure that K-12 educators are ready to work with an ever-diversifying student population, especially older students who come to the United States knowing little, if any, English.
“A really important question that’s raised is what precisely do we mean when we say someone has proficiency in the second or foreign language,” Daniel said.
In other words, does a deep knowledge of grammar equate to language proficiency?
Not necessarily, said Judith Kroll, the director of the Bilingualism, Mind, and Brain Lab at the University of California, Riverside.
“Is the goal to become a monolingual-like native speaker? No, the goal is to become a proficient, bilingual-like speaker of two languages,” said Kroll, a professor of psychology and linguistics.
While it’s typical for children to pick up languages more easily than adults, researchers have struggled to study this phenomenon in laboratory settings.
The latest research findings are based on an analysis of results from a 10-minute online grammar quiz.
To avoid the costly and time-consuming process of following test subjects as they learn a new language over many years, the researchers tried a different approach: They used the online quiz to measure the grammatical ability of many people of different ages who started learning English at different points in their lives, in hopes of gathering enough data to come to some meaningful conclusions.
The response was overwhelming; nearly 670,000 English-learners participated.
In that quiz, the MIT research team focused on grammatical rules most likely to confuse a non-native speaker and wrote questions that could trip them up. To entice more people to take the test, Hartshorne also included questions that were not necessary for measuring language learning but were designed to reveal which dialect of English the test-taker speaks.
After taking the quiz, users answered questions about their current age and the age at which they began learning English, as well as other information about their language background.
As the results rolled in, the researchers spent nine months developing and testing a variety of models to see which was most consistent with their results. They came to the conclusion that grammar-learning ability remains strong until the late teenage years, at which point it drops precipitously.
“Teachers have to be really careful to avoid the assumption that grammatical competence is equivalent to proficiency in English,” said Daniel, who has worked with English-learner students in schools and colleges in the U.S. and abroad.
“It’s certainly more important for teachers to recognize if someone [can] communicate with others, to accomplish their goals on a day-to-day basis, rather than being able to identify the prescriptive grammar rule,” Daniel also said.
Though adults are still good at learning foreign languages, the chances of reaching the level of a native speaker are slim if they begin learning as a teenager or as an adult, the MIT researchers found.
But the research team still does not know what closes the window on the so-called “critical period.”
Hartshorne will embark on several related studies, including one that will compare native and non-native speakers of two additional languages: Spanish and Mandarin.
Like English, those two languages have millions of non-native speakers trying to learn one or the other of them.
“We’re interested in language learning, not specifically English learning,” Hartshorne said.
A version of this article appeared in the May 09, 2018 edition of Education Week as Study: Language-Learning Ability Is Strong Until Late Teens