In a Vietnamese–English preschool, Vietnamese is kept as the anchor language because concepts and reasoning built in a child's strongest language transfer to the second language, while a weakened first language can leave a child with shallow understanding in both. Protecting Vietnamese is therefore not a concession that costs English time; it is part of how English grows well.
This article explains the research behind that position, from additive and subtractive bilingualism to Jim Cummins's interdependence hypothesis and the work of Lily Wong Fillmore on first-language loss. It then turns to practice: what rich Vietnamese looks like in a preschool day, how international teachers can support a language they may not speak, and how the anchor principle applies to children whose strongest language is something else.
Additive and subtractive bilingualism
The Canadian psychologist Wallace Lambert, known for his work on French immersion programmes in Quebec, distinguished in the 1970s between additive and subtractive bilingualism. In additive bilingualism, a second language is learned while the first continues to develop and remains valued, so the child ends up with two languages. In subtractive bilingualism, the second language gradually replaces the first, often because the first has low status at school or in the wider society, so the child ends up exchanging one language for another.
Immersion programmes for English-speaking Canadian children were additive almost by definition: the children's English was the majority language and was never under threat. The same design applied to minority-language children could be subtractive. This difference explains why research on bilingual education sometimes looks contradictory. Outcomes depend heavily on which language is the child's first, how strong it is, and whether school and society support it.
For most children in a Vietnamese bilingual preschool, Vietnamese is in no danger of disappearing from society. The risk is quieter and more personal. In families that push English heavily, sometimes switching the home language to English with limited fluency, children can end up with conversational English and Vietnamese that stops developing at the level of everyday talk. A preschool that keeps Vietnamese rich and valued helps keep the picture additive.
The interdependence hypothesis and what transfers
Jim Cummins proposed that the languages of a bilingual person rest on a common underlying proficiency: knowledge of concepts, of how stories and explanations are organised, of how print works and of how to learn, which is available to both languages once each is developed enough. This is why a child who understands what "half" means, or that a story has a beginning, a problem and an ending, does not need to relearn those ideas in English. She needs the English to express them.
The practical implication is that time spent building concepts and reasoning in the stronger language is not lost to the weaker one. When children in a Vietnamese preschool explore floating and sinking with a teacher who asks rich questions in Vietnamese, they build the concept. When they meet the same experiment in English, they are learning vocabulary for something they already understand, which is much easier than learning a concept and a language at once.
Cummins also described the difference between conversational fluency and the more complex language needed for explanation and learning, often abbreviated as BICS and CALP. The details matter more for primary school, but even in preschool the lesson holds: a child who chats easily in English may still need Vietnamese, or more time, to explain a sequence or argue a point. Teachers should not mistake playground fluency for the full picture.
What happens when the first language weakens
In a widely cited 1991 paper titled "When learning a second language means losing the first", Lily Wong Fillmore reported on language-minority families in the United States whose young children attended English-language preschools. Many of the children shifted rapidly towards English, and parents described losing the ability to talk with their children about anything beyond the basics, because the parents' English was limited and the children's first language had stalled.
The context is different from Vietnam, where Vietnamese is the majority language. But a version of the same risk appears whenever a home language is not the school's main language: for Korean, Japanese or Chinese families in Ho Chi Minh City, and in some Vietnamese families who have decided to speak only English at home. In each case, children may lose the language that connects them with grandparents, cultural traditions and their parents' deepest conversations.
UNESCO has for decades encouraged education that begins in a child's first language, starting from a 1953 report on the use of vernacular languages in education and continuing in later guidance on mother tongue-based multilingual education. The principle behind that guidance applies well to early childhood: children learn best when they understand the language of instruction, and their first language is a foundation to build on, not an obstacle to remove.
What rich Vietnamese looks like in a preschool day
Conversation, not just instruction. Vietnamese in many classrooms is reduced to directions: sit down, line up, eat your rice. Rich Vietnamese includes open questions, explanations, jokes and talk about feelings, so children hear and use complex sentences.
Traditional rhymes and songs. Vietnamese đồng dao and children's songs carry rhythm, tone patterns and cultural memory. Clapping and movement rhymes are excellent for phonological awareness and are among the most loved parts of a day.
Vietnamese picture books and storytelling. Read-alouds in Vietnamese deserve the same care as English ones: good books, expressive reading and real discussion. Oral storytelling of folk tales gives children a shared cultural repertoire.
Respectful forms of address. Vietnamese pronouns encode relationships: cô, con, bạn, anh, chị, em. Modelling them warmly teaches social understanding as well as grammar, and children who use them confidently are learning something English does not offer.
Vietnamese for thinking aloud. When a group solves a problem, such as how to make a ramp so a car goes further, encourage reasoning in Vietnamese: why do you think that, what will happen if, how could we check. This is where concepts are built.
How international teachers can support a language they may not speak
An English-speaking teacher in a Vietnamese preschool can be a strong ally for Vietnamese, even without fluency. The first step is attitude. Children read adults closely, and a teacher who shows interest in Vietnamese words, laughs at her own mistakes and asks children to teach her signals that Vietnamese is valuable. A teacher who treats Vietnamese as background noise sends the opposite message.
Practical steps follow. Learn children's names with their correct tones, and the everyday words children use for their needs. Learn to recognise the Vietnamese pronouns and use them appropriately when referring to colleagues. During co-planning, ask the Vietnamese teacher which concepts will be built in Vietnamese this week so that English activities can build on them rather than repeating them from scratch.
Teachers should also avoid habits that quietly undermine the anchor. Praising English more warmly than Vietnamese, asking children to "say it in English" as if Vietnamese were a lesser answer, or treating Vietnamese circle time as a break for the English teacher all teach children a hierarchy. A team that shares the same respect for both languages gives children a more secure bilingual identity.
Some international teachers go further and take up Vietnamese lessons once they settle. Even a modest level changes the room. The teacher understands more of what children say to each other, can join a Vietnamese song without stumbling, and can follow the gist of a conversation with a grandparent at the gate. Children are often delighted to correct an adult's tones, and in doing so they rehearse the very contrasts they are learning themselves. The teacher's visible effort also shows children that learning a language is slow, normal and worth doing, which is the attitude a bilingual school hopes they will carry for life.
Checking the status of Vietnamese in your own school
Few schools set out to weaken Vietnamese, so it is worth looking for the quiet signals that it has happened anyway. Walk through the building and notice which language appears on the displays parents see first, which language the school uses when it celebrates children's achievements, and whether the Vietnamese book collection is as carefully chosen as the English one. Listen to how adults talk about children: is a child described as "good" because her English is fluent, while a child with rich Vietnamese storytelling goes unremarked?
Look, too, at how time is spent. If Vietnamese sessions are routinely the ones cut when an event or a visitor interrupts the day, or if Vietnamese teachers are mostly asked to manage routines while English teachers lead the planned learning, children will absorb that hierarchy even if no one states it. A short team discussion about these signals, once or twice a year, is often enough to restore the balance.
Families notice these signals as well. When a school shows, in its displays, reports and events, that it values Vietnamese as highly as English, parents are more likely to keep investing in Vietnamese at home, and the anchor stays strong from both sides.
Preparing for primary school in Vietnamese
Most children in Vietnamese bilingual preschools will enter a primary school where reading, writing and mathematics are taught in Vietnamese from Grade 1. Even children heading to international primary schools usually continue Vietnamese as a subject. A strong oral foundation in Vietnamese, with good listening, vocabulary, storytelling and awareness of sounds and tones, is one of the most useful things a preschool can give them.
This does not mean formal reading or writing lessons in preschool. The Ministry of Education and Training has repeatedly cautioned against teaching the Grade 1 curriculum early in kindergartens, and the national preschool programme focuses on readiness through play: interest in books, recognising that print carries meaning, holding a pencil comfortably through drawing, and playing with sounds. Bilingual preschools follow the same principle in both languages.
Teachers can help families understand this, because some parents feel pressure to have children reading before Grade 1. Explaining that rich oral language in Vietnamese is the best predictor of comfortable early reading, and that English literacy builds on the same foundations, often eases that pressure.
When a child's anchor is another language
For a child from a Korean, Japanese, French or other family, the anchor language is the home language, and the school is helping her add Vietnamese and English. The same principles apply, adapted. The school asks families about the child's language at enrolment, encourages them to keep using it richly at home, and avoids advising them to switch to English or Vietnamese to "help" the child, which research suggests often backfires when parents are not fluent.
In the classroom, teachers give such children time, visual support and warm relationships, and accept that understanding of both school languages will grow before speaking does. They make space for the home language in small ways, as described in our article on translanguaging. Over time, these children often become the most linguistically flexible members of the class, and their presence helps every child understand that languages are many and all are worth having.
Whatever the anchor, the message to families is consistent: the language you speak best with your child is the one to keep speaking. School will add languages; home keeps the foundation strong.
Câu hỏi thường gặp
Why not use as much English as possible in a Vietnamese preschool?
Because concepts and reasoning built in a child's strongest language transfer to English, while a weakened first language can leave understanding shallow in both. Rich Vietnamese supports English growth rather than competing with it, as long as English also has meaningful time.
What is the interdependence hypothesis?
It is Jim Cummins's proposal that a bilingual's languages share a common underlying proficiency, so knowledge of concepts, story structure and learning strategies developed in one language is available to the other once that language is developed enough to express it.
Should Vietnamese parents speak English at home to help?
Generally it is better for parents to speak the language they are most fluent and expressive in, usually Vietnamese. Rich conversation in a strong language does more for a child than limited English, and it protects the parent–child relationship as the child grows.
Do bilingual preschools teach children to read Vietnamese before Grade 1?
They should not teach formal reading early. The national preschool programme focuses on readiness through play, such as interest in books, awareness of sounds and tones, and drawing. Strong oral Vietnamese is the best preparation for Grade 1.
Can an international teacher help children's Vietnamese?
Yes. Showing genuine interest in Vietnamese, using names and pronouns correctly, asking children to teach words, and co-planning so English builds on concepts developed in Vietnamese all help. Avoiding praise hierarchies between languages matters just as much.
What if a child's strongest language is neither Vietnamese nor English?
Then that home language is the anchor. The school encourages the family to keep using it richly, gives the child time and support to add Vietnamese and English, and makes small spaces for the home language in class.