Bilingual Education: Benefits, Drawbacks & What Works
“Will both English and Japanese really develop properly?” For many parents, looking into bilingual education brings hope and worry at the same time. Search for it and you will find articles saying it raises cognitive ability sitting next to articles warning about “semilingualism.” Both are written with confidence, which makes it all the harder to know what to make of them.
This article sets out what bilingual education is, then checks what research actually shows about its benefits and drawbacks. From there, it covers the conditions that decide outcomes and what families can do at home.
In this article
What is bilingual education? Growing up through two languages
Bilingual education is the umbrella term for approaches that carry daily life and learning in two languages, aiming for age-appropriate ability in both. What separates it from studying English as a school subject is that language is not only the thing being learned — it is also the tool used to learn.
In Japan, families typically choose among four forms.
| Form | What it looks like | Who carries it |
|---|---|---|
| Immersion | Most of the day at a school or nursery is spent in English | International preschools, etc. |
| One parent, one language (OPOL) | Each parent speaks a different language to the child | Bilingual households |
| English at home | Picture books, songs and everyday talk in English | Parents |
| Combination | Home practice plus a school or class | Family + an institution |
Bilingualism that adds, and bilingualism that replaces
There is one distinction worth holding onto. In 1975 the Canadian psychologist Wallace Lambert set out the difference between additive and subtractive bilingualism1. Additive means a second language is gained while the first is kept; subtractive means the first language is lost as the price of the second. Subtractive outcomes are known to arise where the home language is a minority one in society and there is no opportunity to learn through it1.
For a family living in Japan and using Japanese at home and in the community, the structure tends to favour the additive case. Most of the cautions below come down to a single question: how do you make sure the languages stack up rather than swap over?
What research actually says about the benefits and drawbacks
First, the benefits and drawbacks as they are usually described.
| Commonly cited benefits | Commonly cited drawbacks |
|---|---|
| Able to communicate in two languages | The two languages get mixed |
| Deeper understanding of other cultures | Vocabulary can look small for a while |
| Wider educational and career options | Worry about the mother tongue |
| Cognitive benefits | A heavier learning load |
How far can you really claim it “makes children smarter”?
The single most common claim in articles on bilingual education is that it boosts cognitive function. At the centre of that view is Professor Ellen Bialystok of York University in Canada. Writing in Child Development Perspectives (2015), she argued that the experience of managing two languages trains how attention is directed, and is bound up with the development of executive function — the ability to control attention and behaviour toward a goal4.
Later scrutiny, however, has been more cautious. A team from the University of Stavanger and the University of Oslo published a meta-analysis in Psychological Bulletin (2020) pooling 143 group comparisons (583 effect sizes) in children aged 18 and under. A bilingual advantage in overall executive function was statistically detectable, but the effect size was g = 0.06 — marginal — and indications of publication bias were reported5. After correction, only switching remained significant5.
In other words, the grounds for asserting that bilingual education makes children smarter are not currently strong. As educators, we would rather not overstate this. That said, even if the cognitive bonus is small, it takes nothing away from the value of being able to use two languages. More books you can read, more people you can talk to, more paths open to you — these are not side effects. They are what bilingual education is for.
What research says you need not worry about
Conversely, several of the things described as drawbacks are contradicted by the evidence. Professor Krista Byers-Heinlein of Concordia University and Professor Casey Lew-Williams of Princeton University reviewed research on bilingual infants and toddlers in LEARNing Landscapes (2013)6:
- Language delay — bilingual children are not more likely than monolingual children to have language difficulties, show delays, or be diagnosed with a language disorder
- Small vocabulary — counting only one language can make vocabulary look small, but measured as “conceptual vocabulary” across both languages it matches monolinguals
- Mixing — code-mixing is a normal part of bilingual development, and a resourceful way of using every word a child has to get a message across
Parents often raise the worry that English and Japanese come out jumbled together. That is best understood as a sign development is going well. Language does vary from child to child, though, so if something continues to concern you, please consult a specialist.
Before worrying about “semilingualism”: the mother tongue as foundation
The drawback that comes up without fail is the fear of ending up half-competent in both languages. Behind that worry is the theory Professor Emeritus Jim Cummins of the University of Toronto set out in Review of Educational Research in 19792.
Cummins proposed that although two languages look separate on the surface, beneath them lies a common cognitive foundation, and that concepts and literacy built in the first language transfer to the second. His interdependence hypothesis holds that how well the first language has developed at the point intensive exposure to the second begins is bound up with academic development afterwards2.
Equally telling is his distinction between the language of everyday conversation (BICS) and the abstract language demanded by academic learning (CALP)3. Speaking fluently and being able to think and learn in that language are different capacities.
The term “semilingual” itself is now generally avoided in research, since it works as a label locating a deficit in the child. It is more accurate to ask which ability, in which language, in which setting, has not yet developed.
The surest thing a family can do is not to cut back on conversation and reading aloud in the home language. Adding English time and subtracting Japanese time are not the same thing.
What decides the outcome: quantity, and who you speak with
So what separates success from disappointment? What multiple studies show consistently is that the quantity and quality of input matter more than the age you start.
How many hours is the child actually in the language?
Researchers often treat exposure of roughly 10–25% of waking hours to each language as the threshold for counting a child as using it6. A classic study of input and lexical learning in bilingual infants (Pearson et al., Applied Psycholinguistics, 1997) likewise found that the less a language is heard, the more slowly vocabulary in it grows7.
That percentage is a convenient research cut-off, not a guarantee that meeting it produces a bilingual child6. It is still worth doing the arithmetic. Take 12 waking hours a day: 10–25% is roughly one to three hours. Set against that, one hour a week at a class is clearly not going to reach it.
Who the child speaks with, and in which language
One large study shows how much the family’s language pattern matters. Professor Annick De Houwer surveyed 1,899 families in Belgium (Applied Psycholinguistics, 2007) and found that the proportion of children who actually spoke the minority language varied sharply with what the parents did at home8.
| Language pattern at home | Children who spoke the language |
|---|---|
| Both parents use the language at home | about 97% |
| Both parents use both languages | about 79% |
| Only one parent uses it (one parent, one language) | about 74% |
| One parent uses both; the other only the majority language | about 36% |
De Houwer concludes that the widely known OPOL approach is neither a necessary nor a sufficient condition8.
An important caveat belongs here. The families studied were ones where a parent spoke the minority language. For a Japanese-speaking household raising English, the premise is different. Securing one to three hours of English input a day inside the home is rarely realistic, which is exactly why a school or class outside the home becomes the practical source of that input. On what a preschool is in the first place, see What is a preschool? How it differs from nurseries and kindergartens.
People before screens
Quality of input has clear findings behind it too. Infants do not readily learn language from video, and opportunities to interact with several different speakers are linked to vocabulary learning6. In an experiment by Professor Patricia Kuhl and colleagues at the University of Washington (PNAS, 2003), infants who interacted face to face with a speaker of a foreign language learned to discriminate its sounds, while those who heard exactly the same audio via video or sound alone showed no effect9.
This does not mean English videos and audio have no value — only that leaving them running rarely amounts to learning. They come to life as material to watch alongside your child while talking about it. We cover this in more detail in When should babies start English?
At what age should you start?
There is no single right answer to the question of what age to begin. A research review of the critical-period hypothesis in second-language acquisition (Nanzan University, Shikano, 2018) concludes that the simple view of a single critical period up to age X is hard to support, and that the sensitive period differs by type of ability — pronunciation, vocabulary, grammar10. Materials from Japan’s Ministry of Education also state that no clear critical period has been confirmed where English is learned as a foreign language11.
That is not to say starting early is pointless. Infancy is a period of heightened sensitivity to sounds outside the native language9. And the pre-school years have a practical advantage: before schoolwork and lessons crowd the calendar, it is easier to secure a sustained block of English in daily life.
What matters is less the age you began than whether the arrangement is one you can sustain comfortably. Language develops at each child’s own pace, and responses differ widely even at the same age. There is no need to feel it is already too late.
How this works at Laurus International School
Substantial input, real interaction with people, and an additive shape that does not cut into Japanese — the preschool at Laurus International School of Science is built around putting these into daily practice.
Children can join from 18 months in an all-English environment, with classes grouped by developmental stage: Newton (from 1.5), Galileo (2–3), then Da Vinci, Darwin and Einstein as learning continues into kindergarten. A class of around 20 children is staffed by one homeroom teacher and two to three childcare staff, which keeps one-to-one interaction available12.
What stands out is that English is not the object of study but the tool for it. Wondering why something happens, predicting, experimenting, observing to check — running science activities in English ties words to situations that mean something. Phonics and vocabulary, early mathematics, rhythmic music, physical education and art all take place in the same English environment12.
See the preschool curriculum →
In closing
Discussion of bilingual education tends toward large claims in both directions. Held against the research, what is solid may be more modest than expected. The cognitive benefits have been overstated5, while most of the worries — mixing, apparent gaps in vocabulary — turn out to be a normal part of development6.
What decides the outcome is not the age of starting but how much input accumulates, and through whose company68. And keeping the Japanese foundation intact is the condition under which two languages stack up rather than swap over12.
Laurus holds school visits and information sessions on a rolling basis13. Please feel free to use them as a chance to see for yourself how your child responds in an English-speaking environment.
Questions & Answers Frequently Asked Questions
8 questionsThe benefits are being able to communicate in two languages, a deeper understanding of other cultures, and wider options later on. The drawbacks usually cited — a small vocabulary, mixed languages — fall within the normal range of development according to research6. What actually warrants care is a subtractive situation where the mother tongue stops developing as the price of the second language, and that is avoided by protecting time spent talking and reading in it1.
It is the umbrella term for approaches that carry daily life and learning in two languages, aiming for age-appropriate ability in both. In the United States it has historically referred to transitional programmes that teach immigrant children in their home language while gradually increasing English instruction; in Japan it generally refers to developing both Japanese and English.
There is no single right answer. Research reviews find that the sensitive period differs by type of ability — pronunciation, vocabulary, grammar — so a single “by age X” deadline is hard to support10. Materials from Japan’s Ministry of Education likewise state that no clear critical period has been confirmed where English is learned as a foreign language11. Rather than the starting point, judge by whether the arrangement is sustainable.
There is immersion, where a child enters an English environment at a school or nursery; one parent, one language, where each parent speaks a different language; English at home through picture books and songs; and combinations of these. Rather than asking which is best, it helps to choose by where the necessary volume of input will come from.
Yes. A survey of 1,899 families concluded that one parent, one language is neither a necessary nor a sufficient condition for transmitting a minority language8. A division of labour works fine: parents talk richly in Japanese while English input arrives from a school or class, from books and from songs.
Research has not found that bilingual children are more likely to have language difficulties6. Vocabulary in one language can look small temporarily, but conceptual vocabulary across both matches monolinguals6. The thing to watch is the opposite: adding English time in a way that reduces conversation and reading aloud in Japanese.
In most cases there is no cause for concern. Code-mixing is a normal part of development and a resourceful way of using every word a child has to get a message across6. With time, children come to select the language to suit the listener. Development does vary, so if something continues to concern you, please consult a specialist.
Yes, if the environment is designed deliberately. The benchmark often used is exposure of around 10–25% of waking hours to the language6. On a 12-hour day that is one to three hours, which is often hard to secure at home alone, so combining home with a school or class is the realistic route.
- Educating Language-Minority Children — National Research Council / National Academies Press, 1998 (contains Lambert 1975 on additive and subtractive bilingualism) National Academies Press (1998) · Lambert 1975
- Linguistic Interdependence and the Educational Development of Bilingual Children — Jim Cummins, Review of Educational Research, 49(2), 222–251, 1979 Jim Cummins · Review of Educational Research (1979)
- Cognitive/Academic Language Proficiency, Linguistic Interdependence, the Optimum Age Question and Some Other Matters — Jim Cummins, Working Papers on Bilingualism, 19, 1979 Jim Cummins · Working Papers on Bilingualism (1979)
- Bilingualism and the Development of Executive Function: The Role of Attention — Ellen Bialystok, Child Development Perspectives, 9(2), 117–121, 2015 Ellen Bialystok · Child Development Perspectives (2015)
- Is bilingualism related to a cognitive advantage in children? A systematic review and meta-analysis — Gunnerud et al., Psychological Bulletin, 146(12), 1059–1083, 2020 Gunnerud et al. · Psychological Bulletin (2020)
- Bilingualism in the Early Years: What the Science Says — Krista Byers-Heinlein & Casey Lew-Williams, LEARNing Landscapes, 7(1), 95–112, 2013 Byers-Heinlein & Lew-Williams · LEARNing Landscapes (2013)
- The relation of input factors to lexical learning by bilingual infants — Pearson, Fernández, Lewedeg & Oller, Applied Psycholinguistics, 18(1), 41–58, 1997 Pearson et al. · Applied Psycholinguistics (1997)
- Parental Language Input Patterns and Children's Bilingual Use — Annick De Houwer, Applied Psycholinguistics, 28(3), 411–424, 2007 Annick De Houwer · Applied Psycholinguistics (2007)
- Foreign-language experience in infancy: Effects of short-term exposure and social interaction on phonetic learning — Kuhl, Tsao & Liu, PNAS, 2003 Kuhl, Tsao & Liu · PNAS (2003)
- A review of the critical-period hypothesis in second-language acquisition — Nanzan University (Midori Shikano, 2018) Nanzan University (2018)
- Materials on the critical period in foreign-language education — MEXT MEXT · Central Council for Education
- Preschool Curriculum — Laurus International School of Science Laurus · Preschool Curriculum
- School Visits & Information Sessions — Laurus International School of Science Laurus · School Visits