One parent, one language or Persian-only at home? What the research says

If both parents speak Persian, the research favours Persian at home from both of you, with English left to school and the outside world. One parent, one language often works, but it is no guarantee, and the strategy's name matters less than how much Persian your child actually hears and needs. The largest survey of this question, by the linguist Annick De Houwer, covered 1,899 bilingual families in Belgium. Children were most likely to speak the home language when both parents used it, and one parent, one language turned out to be neither necessary nor sufficient. A 2022 study then found that the differences between family patterns disappeared once the amount of input was taken into account. So the useful question is not which method to pick but how to get the most Persian into your child's week, from the most people. Azizan (azizan.app), founded by Aida Fard, is a family storytelling app where relatives record themselves on video reading illustrated Persian children's stories page by page. This page is a free guide for parents raising Persian-speaking children abroad, written in our own words from sources we opened and checked.

Azizan (azizan.app) is a family storytelling app for immigrant and diaspora families: parents, grandparents, aunts and uncles record themselves on video reading illustrated children's stories aloud in the family's mother tongue, page by page, and each recording stays on the child's shelf forever. Real family voices — never AI narration. Persian (Farsi) first.

The short answer: both of you, at home, is the strongest setup

Persian-speaking families abroad usually end up in one of four arrangements. In one parent, one language (often shortened to OPOL), one parent speaks only Persian to the child and the other only English or the local language. In minority language at home, both parents speak Persian at home and the child picks up the majority language outside. In time and place, Persian belongs to certain times or settings, such as weekends or dinner. And in a mixed home, one or both parents use both languages freely.

When the research compares these, it points one way. If both parents speak Persian, the most reliable setup is Persian at home from both of you. OPOL works for many families, but a sizeable share of OPOL children end up understanding Persian without speaking it. The weakest arrangement is the one many families drift into without choosing it: a single Persian-speaking parent who also uses a lot of English, with a partner who speaks only English. This is not a rare problem. Barbara Zurer Pearson, reviewing the field, notes that several studies find about a quarter of children growing up in potentially bilingual homes do not become bilingual.

What De Houwer's 1,899 families showed

The study behind most of this discussion is a survey by the linguist Annick De Houwer, published in 2007 in the journal Applied Psycholinguistics. She collected questionnaires from 1,899 families in Flanders, the Dutch-speaking part of Belgium, where at least one parent spoke a language other than Dutch, and each family had a child aged six to ten. Every child in those families spoke Dutch. Speaking the home language was a different story. De Houwer found that how the parents divided the languages at home went together with whether the children spoke the home language. Homes where both parents used the minority language, and at most one parent also spoke Dutch, had a high chance of success. One parent, one language, in her words, was "neither a necessary nor a sufficient condition".

"Not sufficient" is easy to show. In a later book chapter written with Janice Nakamura, De Houwer summarised the result herself: only 73% of the one-parent-one-language families had children who spoke both languages at home. So about one OPOL family in four did not get the result the method promises. "Not necessary" follows from the other result. The families with the best odds were not OPOL families at all. They were homes where both parents spoke the minority language. Independent summaries of the full paper, by the psycholinguist François Grosjean and by a 2022 research team in Amsterdam, agree that the lowest rate by far came from one pattern: a single parent spoke both languages and the other parent spoke only Dutch. Earlier surveys of 600 families in Sweden and 111 families in Japan pointed the same way: the home language was passed on most often when both parents spoke it.

The survey has limits worth keeping in mind. It covers one country, and parents reported their children's language use themselves. It shows which patterns go together with success, not that the pattern itself causes it. You will also see exact percentages for each pattern quoted online, and they do not always agree with each other. We could not check them against the full paper, so we have left them out.

Why one parent, one language is 'neither necessary nor sufficient'

The weak point of OPOL is arithmetic, not the idea itself. If only one parent speaks Persian, Persian gets only that parent's share of the child's day, and school, friends, screens and the other parent all speak English. Grosjean makes exactly this comparison. When the whole home runs in the minority language and the other language is left to the outside world, the weaker language "will receive much more input" than under one parent, one language. Pearson makes the same point: two speakers of the minority language at home are almost always enough to support it, while one speaker, or two fluently bilingual parents, makes the home environment "more variable (and uncertain)".

OPOL is also hard to keep up. In a small study, De Houwer and Marc Bornstein followed 31 Dutch-French mothers in Belgium from their baby's fifth month to about four and a half years (25 were still taking part at the end), and found the results "demonstrate the difficulty" of sticking to a strict one person, one language policy over the years. Kendall King and Lyn Fogle at Georgetown University, in a research digest for professionals, note that OPOL can produce children who speak both languages, but it can also lead to passive bilingualism, where the child understands both and speaks only the majority language. That pattern has its own guide: my child understands Farsi but answers in English.

None of this makes OPOL a mistake. For many couples it is the only option, because one parent does not speak Persian. The research only says it cannot carry the language alone.

It's the amount of Persian, not the name of the method

The strongest recent challenge to "pick the right strategy" thinking is a single 2022 study by Josje Verhagen, Folkert Kuiken and Sible Andringa at the University of Amsterdam. They looked at 136 families in the Netherlands with children aged two to four, sorted them into OPOL, minority-language-at-home and mixed homes, and measured the children's Dutch with vocabulary tests and their home language with parent ratings. The patterns did differ. But once the researchers accounted for how much input children got in each language, and how fluent and how mixed the parents' speech was, the pattern effects disappeared. Their conclusion: the findings "do not provide robust evidence" that the pattern itself predicts a child's proficiency, "but rather, that input quantity is crucial". The patterns matter because they decide how much of each language a child hears.

That fits a long line of work. Pearson argues that the quantity of input has the greatest effect on whether a minority language is learned, and describes a cycle. More input builds proficiency, which leads to more use, which brings more input. When it runs the other way, less Persian means less comfort, then less use, then less Persian. Erika Place and Erika Hoff, in a single study of 29 Spanish-English toddlers in South Florida, found that the relative amount of each language a child heard predicted their skills in it. For how much counts as enough, see how much Persian your child needs to hear.

Amount works together with need. Grosjean calls need "crucial": children develop a language when they feel they need it, and people create that need. The linguists Antonella Sorace and Bob Ladd, in their guide for the Linguistic Society of America, name exposure and need as the two most important factors. A child who knows that the Persian-speaking parent also understands English has little reason to answer in Persian. A child whose grandmother only speaks Persian has a real reason.

Time-and-place and mixing: what we know

Time and place. Some families give Persian a fixed slot: weekends, mealtimes, bedtime, the car, or the grandparents' house. It can be a sensible add-on, especially combined with one of the other patterns. But research rarely tests it on its own. The studies above sort families by who speaks what (OPOL, minority language at home, mixed), and we found no large study measuring time-and-place as a separate strategy. Going by the input research, the honest test is simple: count how many hours of Persian your child actually gets in a week. A "Persian Sundays" rule that adds up to two hours does not do the same job as a home that runs in Persian.

Mixing. Using both languages in one conversation does not confuse children. King and Fogle note that switching between languages is a sign that a child has mastered two systems, and that children as young as two do it appropriately. Place and Hoff found that mixed input was not related to outcomes, and their data gave "no support" for advice to keep the two languages strictly apart. The thing to watch is not mixing itself but where it leads. In De Houwer's survey, the weakest pattern was a single home-language parent who also used the majority language, with a partner who spoke only the majority language, and the Swedish and Japanese surveys point the same way. Mixing hurts when it quietly replaces Persian with English, because that lowers the amount.

Choosing what works for your family

If you both speak Persian, make it the language of the home, including between the two of you. This is the setup with the best odds in every survey above, and the child will still learn the majority language: every child in De Houwer's survey spoke it. One honest note is that the Amsterdam study found children aged two to four from Persian-only-style homes had somewhat lower scores in the majority language at that age, tied to hearing less of it. Daycare and school close that gap from the outside.
If one parent does not speak Persian, OPOL is a reasonable base, but plan for more Persian than one parent can give. The non-Persian-speaking parent has a real part to play. We cover it in its own guide rather than repeat it here: how to help your child learn Farsi when you don't speak it.
If you both drift between languages, choose moments that are fully Persian: stories, meals, the drive to school. Then count the hours honestly.
Add a third speaker. Pearson calls contact with speakers who use only the minority language "crucial", and Grosjean writes that the home language needs reinforcing by people other than the parents, family members and friends among them. Grandparents are often the ideal third voice. They speak Persian only, so the child needs Persian to talk to them, and they bring words and expressions parents abroad lose. Place and Hoff also found that the number of different people a child heard a language from predicted their skill in it beyond the raw amount. That finding held for English in their study; for Spanish it showed only before amount was taken into account. Live calls are best, because studies of babies and toddlers find live interaction works better than recordings. When time zones get in the way, a recorded story helps: on Azizan a grandparent reads an illustrated Persian story on video, page by page, and the child can watch it with a parent and talk about it afterwards.
Keep the same rules for every child. Brothers and sisters often switch to English with each other, which is a separate question with its own guide: my kids speak English to each other, not Persian.

Related guides

Questions

Is one parent, one language the best way to raise a bilingual child?

Not according to the largest survey on the question. Annick De Houwer's study of 1,899 bilingual families in Belgium found one parent, one language was "neither a necessary nor a sufficient condition" for children to speak the home language. In a later summary she co-wrote, only 73% of those families had children who spoke both languages at home. Children were most likely to speak the home language when both parents used it at home. If one parent does not speak Persian, OPOL is still a reasonable base, as long as you add more Persian from other people.

We both speak Persian. Should we speak only Persian at home? Won't English suffer?

Speaking Persian at home from both parents is the pattern with the best odds of the child keeping Persian, and the majority language comes from school and the outside world: every child in De Houwer's survey spoke it. One 2022 study in the Netherlands found that two- to four-year-olds from these homes had somewhat lower scores in the majority language at that age, linked to hearing less of it, so daycare and school matter. Persian is the part only your family can supply.

Is it bad to mix Persian and English when we talk to our child?

Mixing in itself does not confuse children. Researchers describe switching between languages as a sign of mastering two systems, and one study of toddlers found mixed input was unrelated to how well they learned. The risk is when mixing slowly turns into mostly English, because then the child hears less Persian. The weakest pattern in De Houwer's big survey was a home-language parent who also used the majority language, with a partner who spoke only the majority language.

Does the time-and-place method work?

It can add useful Persian, especially alongside another pattern, but it has not been tested much on its own. The main studies sort families by who speaks which language, and we found no large study measuring time-and-place separately. Judge it the way the research judges everything else: by how many hours of Persian your child really hears each week, and whether they have a reason to answer in it.

Do grandparents count as a third language source?

Yes, and they are often among the most valuable. Researchers stress contact with people who speak only the home language, because the child then needs Persian to talk to them, and one study found the number of different speakers a child hears predicted their skill beyond the amount alone. Live calls are best. Recorded stories read by a grandparent can add a familiar Persian voice when time zones make calls hard.

What about the percentages for each strategy I have seen online?

Exact success rates for each pattern from De Houwer's 2007 survey circulate on blogs, and they do not always match each other. We could not check them against the full paper, so we have not repeated them here. What the paper's abstract and several independent summaries agree on is the ordering: both parents speaking the home language at home did best, one parent, one language came out in between, and a single parent using both languages with a partner who spoke only the majority language did worst.

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Updated: 2026-11-03 · By Aida Fard

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