How Age Shapes Second Language Acquisition
When—and How—Is English Acquired?

This is the case of children who grow up hearing two languages, such as Japanese and English, on a daily basis from birth. At this stage, a single-language phonological system has not yet fully solidified. Children hear large amounts of both languages and build patterns for each language’s sounds, words, meanings, and sentence structures.

For example, when a child hears dog, they do not translate it into “inu.” Instead, dog and an actual dog connect directly, and the Japanese word “inu” and an actual dog also connect directly. The defining feature is not studying English as a foreign language, but building two languages simultaneously through daily life.

This is the case in which a second language enters daily life after Japanese has developed to some degree—for example, when a family moves to an English-speaking country. If a 4-year-old enters an English-language preschool, they may not understand Come here. Sit down. Your turn. at first. But as they experience the same words in the same situations day after day, English and meaning begin to connect directly.

Japanese has already started to develop, but speech perception is still highly plastic. With abundant English experience in daily life, English sounds, words, meanings, and sentence patterns begin to form as a second language system.

For children who move to an English-speaking country around elementary school age and attend local schools, the Japanese phonological system is already fairly well established. Even after entering a local school, they may still be unable to segment the English speech stream well enough at first and feel that they can barely understand what is being said. Comprehension develops first, while speech is slow to emerge—the so-called silent period.

For returnee children, even if they hear English all day at school, it is common for home life to be in Japanese with family. As a result, it takes time to accumulate enough English speech input, and it is more realistic to expect that it may take about six months to a year before English starts to sound like connected language.

What matters is that this period is not a time when nothing is happening. As children hear large amounts of English, they learn English phonemes, syllables, stress, and rhythm, and the speech stream that once sounded continuous gradually begins to break into words. The silent period can be understood as a time when English speech perception and the lexicon are being built below the surface.

When students study abroad in an English-speaking country during high school or college, Japanese phonology is already firmly established. At the same time, learners who have studied English in junior high and high school often have substantial explicit knowledge of English words and grammar. They can compare what they hear with words and sentence patterns they already know.

Study abroad also often means more than just school: conversations with host families, shopping, TV, and time with friends may all happen in English from morning to night. That daily life as a whole becomes a source of massive English input is the major difference from returnee children. As a result, after a few months, learners may find that they can hear word boundaries more clearly and follow the overall meaning.

In other words, it is not simply true that younger is always faster when comparing returnee children and study-abroad students. The speed of speech perception development depends heavily not only on age, but also on the knowledge learners already have and how much English itself they process each day.

What must be considered separately from returnee children and study-abroad students is the case of learning English within Japan. In Japan, most of daily life—at home, at school, while shopping, and in conversations with friends—takes place in Japanese. For example, a student who studies English for a few hours a week in a Japanese junior high school is an EFL learner. Once class ends, almost all of life returns to Japanese.

The central challenge in an EFL environment is not whether children have the ability to acquire English, but that the amount of natural English they process is overwhelmingly small.

However, living in Japan does not mean that English speech perception cannot develop. As Flege’s (1995) Speech Learning Model (SLM) suggests, the mechanisms of speech learning remain available throughout life. The issue is not age alone, but what kind of speech input a learner experiences and how much of it.

Even in an EFL environment, if children hear large amounts of English every day, they can experience the distribution of English sounds. Over several years, the difference becomes enormous between a child who hears English only in a 50-minute class once a week and a child who is exposed to 1–2 hours of pure English audio at home every day.

Moreover, regular use of English videos, podcasts, audiobooks, and children’s books can greatly expand an English input environment even while living in Japan.

It is not appropriate to divide English speech perception development into possible and impossible based on age alone. In Flege & Bohn’s (2021) revised Speech Learning Model (SLM-r), the speech-learning mechanisms used in first-language acquisition remain available later on, and L2 sound systems can also be reorganized through experience.

There is no need to assume that once the preschool years are over, children can no longer acquire English sounds. Starting early certainly has advantages. But there is still room to change how English is heard in childhood, in adolescence, and even in adulthood.

To sum up, even though we use the same phrase “acquire English,” the conditions can differ greatly. Simultaneous bilingual children build two languages at the same time as languages of daily life. Sequential bilingual children encounter a second daily-life language after the first language has begun to develop. Returnee children and study-abroad students acquire a second language within an L2 environment after their first language is already in place.

In an EFL environment, often represented by the grammar-translation method, exposure to natural English tends to be limited. So when children acquire English in Japan, what matters is not only the age at which they start, but also how much environment can be created from that age onward for them to experience large amounts of English itself.

Approaches such as English at Home can use age-appropriate tools: audio-centered exposure for preschoolers, audio plus reading for school-age children, and written language, knowledge, inference, and explicit study from adolescence onward. The most effective methods change with age. But what remains true at every age is not just knowledge about English, but the need to process large amounts of English itself and accumulate patterns of English sounds, words, meanings, and sentence structures.

There are advantages to starting early, but even a later start still leaves room for learning.