The clearest advantage is academic. Children in well-run bilingual programs read better in English than comparable children who are not, and the effect is large enough to matter: in the strongest study available, roughly seven to nine months of extra learning by eighth grade. The cognitive advantages you have probably heard about, the ones involving multitasking and brain training, rest on far weaker evidence than most articles admit.
That gap between the two claims is worth understanding before you choose a program. One of them survived a randomised trial. The other has been failing to replicate for a decade.
The Benefits of Bilingual Education That Hold Up Under Testing
Most research on bilingual education has a selection problem. Families who choose these programs differ from families who do not, so better outcomes may reflect the families rather than the schooling.
Portland Public Schools solved that problem by accident. Demand for immersion places exceeded supply, so seats were allocated by lottery. Jennifer Steele and colleagues used seven cohorts of applicants, 1,946 of whom were genuinely randomised, and compared lottery winners with lottery losers. Same families, same motivation, different schooling.
The results, published in the American Educational Research Journal in 2017, showed reading gains of 13 to 22 percent of a standard deviation by fifth and eighth grade, which the authors put at seven to nine months of learning. Students classified as English learners were three to four percentage points likelier to be reclassified out of that status by sixth and seventh grade, and the effect was stronger when the child’s home language matched the program’s partner language.
Now the part the promotional pages leave out. The same study found little benefit in mathematics or science. Not harm, but not gain either.
That matters, because the common claim is that bilingual education lifts everything. It does not. What it reliably lifts is reading:
- Reading gains appear by fifth grade and grow by eighth.
- Maths and science show no measurable gain and no measurable loss.
- English learners exit that classification sooner.
- The gain is larger when the program language is the language spoken at home.
- The findings apply to families who applied to a lottery, not to every family.
What Counts as Bilingual Education
The term covers several different models, and they are not interchangeable. This is where most parent confusion starts.
| Program model | How it works | What the evidence shows |
|---|---|---|
| Two-way dual language immersion | English speakers and speakers of the partner language learn together, with instruction split between both | Strongest causal evidence. Reading gains by fifth and eighth grade |
| One-way immersion or maintenance | Instruction continues in both languages for years, aimed at full literacy in each | Grouped with two-way in the lottery study. Same reading gains |
| Transitional | Home language used as a short bridge, then instruction shifts fully to English within a year or two | Not directly tested by the lottery studies. Home language literacy stops developing at the switch |
Scroll sideways to see the full table
The distinction that matters is how long instruction continues in both languages. A program that treats the home language as a temporary bridge gives a child a year or two of support and then stops. A program built to develop both languages keeps going, which is what the long-running studies were measuring. We cover the mechanics of these models in more detail in our guide to dual language immersion programs.
The Cognitive Benefits of Bilingualism Are Weaker Than You Have Been Told
This is the section other pages skip, and skipping it is why parents feel misled later.
The standard claim was that bilingual children develop stronger executive function, the machinery behind switching attention, holding information in mind, and ignoring distractions. It was appealing and it was widely reported. It has not held up.
In 2015, Angela de Bruin, Barbara Treccani and Sergio Della Sala showed in Psychological Science that studies finding a bilingual advantage were far likelier to be published than studies finding nothing. The literature was partly measuring what editors chose to print.
Then the meta-analyses arrived. Minna Lehtonen and colleagues pooled 891 effect sizes from 152 adult studies in Psychological Bulletin in 2018. Before correcting for publication bias, a very small advantage appeared in inhibition, shifting and working memory. After correcting for it, nothing remained. They also found a small disadvantage in verbal fluency, likely because each language gets less individual use.
For children, Hilde Lowell Gunnerud and colleagues analysed 583 effect sizes in 2020. The overall advantage was significant but marginal, g = 0.06, with signs of publication bias, and it appeared mainly in studies of middle-class children and in work from one particular lab.
One thing did survive. In that same analysis, an advantage in switching between tasks held up after correction. So something may be there. It is small, it is specific, and it is nothing like the brain-training claim in circulation.
None of this makes bilingual education a bad choice. It means the reason to choose it is reading, literacy and access to a language, not a cognitive upgrade.
What This Means for Parents Choosing a Program
Four things follow from the evidence that most articles on this topic will not tell you.
- Judge a program by its reading outcomes, not its brain claims. If a school’s pitch leans on executive function and multitasking, it is selling the weakest part of the evidence. Ask what happens to reading scores by fifth grade.
- Ask how many years instruction continues in both languages. This is the single variable that separates the programs the research supports from the ones it does not.
- A home-language match changes the size of the benefit. The Portland effects were stronger for English learners whose home language was the program’s partner language. A Spanish-speaking family choosing a Spanish program is in a different position from an English-speaking family choosing one.
- Expect flat maths results and do not panic. No gain is the documented outcome, not a warning sign. Families who expect improvement across every subject often pull children out at exactly the wrong moment. The same pattern shows up in why bilingual children struggle in school, where an early dip gets misread as failure.
How to Evaluate a Program Before You Enroll
Open days are designed to be persuasive. These five questions get you past the brochure, and every one of them comes straight out of the evidence above.
- How many years does instruction continue in both languages? If the answer is one or two, you are looking at a transitional model. That is not what the reading studies measured.
- What share of the day is in each language, and does it shift by grade? Programs commonly run a 90/10 or 50/50 split, often starting heavier in the partner language and moving toward balance. Any answer is fine. Not having one is not.
- What do your fifth-grade reading scores look like, and compared with which children? Fifth grade is where the effects first showed up, so it is the first honest checkpoint. Compared with whom matters more than the number.
- Are the teachers certified for the grade level as well as fluent in the partner language? Both, or the academic content suffers while the language holds up.
- What happens if we join in third grade instead of kindergarten? Some programs accept later entry with support and some do not. A school that has not thought about it has not thought about your child. Starting later is not the barrier parents assume, which we cover in what age is best to learn a second language.
One question not to bother asking: whether the program improves focus or multitasking. Every school will say yes. The answer tells you nothing, because the underlying evidence does not support a confident answer either way.
What to Do If There Is No Bilingual Program Near You
Most families do not have a dual-language school within reach. The relevant question is whether the same mechanism works outside a full program.
There is direct evidence that it can. Geoffrey Borman and colleagues ran a multi-site randomised controlled trial of one-to-one literacy tutoring delivered in Spanish to struggling Spanish-speaking first graders, published in the American Educational Research Journal in 2020. Students who received it outperformed the control group on Spanish literacy measures by roughly half a standard deviation.
The honest caveat is important. That trial did not find a significant effect on the English measure. Home-language tutoring built home-language literacy. It did not automatically transfer.
So the realistic framing is this. Sustained instruction in a child’s home language builds real literacy in that language, which is the foundation the long-term bilingual outcomes are built on. It is not a shortcut to English scores, and anyone who tells you it is has overstated the case.
What School Owns and What Tutoring Owns
School owns the academic content. A child learns fractions, photosynthesis and essay structure in whichever languages the school uses, and no outside support replaces that volume of instruction.
Tutoring owns the language the school has stopped developing. In an English-only classroom, a child’s home language usually plateaus at conversational level while their English becomes academic. Structured instruction is what keeps the home language growing into reading and writing rather than staying spoken. Our online tutoring covers reading, math and world languages in more than 15 languages, one-to-one or in small groups, with certified bilingual educators.
The thing to avoid is treating home-language sessions as casual conversation practice. Conversation maintains what a child already has. It does not build the academic vocabulary that the research outcomes depend on.
What to Expect, and When
Grades one to three. Expect little visible difference, and possibly a dip on English-only measures. This is the stage where the evidence has nothing encouraging to show, and where most families quit.
Grades four and five. The Portland reading effects first became measurable at fifth grade. This is the earliest point at which the decision starts to look like it was worth it.
Grades six to eight. Effects grew rather than faded, reaching the equivalent of roughly nine months of learning by eighth grade. English learners were also exiting that classification sooner by this stage.
The timeline is the point. Every documented benefit in this post came from programs measured over years. There is no version of this that pays off in a term.
The Honest Verdict
Bilingual education has one well-evidenced academic advantage, and it is a real one: better reading, appearing by fifth grade and growing through eighth, with no cost to maths or science. The cognitive claims are far shakier and should not be the reason you choose anything.
If your child is in an English-only classroom and their home language has stopped growing, that is the gap worth closing. Book a trial class and we will assess where their reading sits in both languages before recommending anything.
Frequently Asked Questions
What are the advantages of bilingual education?
The best-evidenced advantage is stronger reading. A randomised study in Portland found gains worth seven to nine months of learning by eighth grade, with no loss in maths or science. English learners also exited that classification sooner. Cognitive claims about multitasking are far weaker.
Does bilingual education help academically?
Yes, in reading specifically. The gains appear by fifth grade and grow through eighth. Mathematics and science show no measurable gain and no measurable loss. Judging a program by whether it improves every subject sets an expectation the research does not support.
Is bilingual education good for cognitive development?
The evidence is much weaker than commonly reported. Meta-analyses correcting for publication bias found no reliable executive function advantage in adults, and only a marginal one in children. An advantage in task-switching did survive correction, so something small may be real.
Will bilingual education confuse my child or delay their speech?
No. Mixing languages within a sentence is a normal feature of bilingual development rather than a sign of confusion. Children learning two languages reach major milestones on broadly the same timeline as children learning one.
Will my child fall behind in English?
Not in the long run. Early grades may show no advantage or a slight lag on English-only measures, which is why the studies that follow children for years reach different conclusions from those measuring a single test score.
What is the difference between dual language and transitional programs?
Dual language programs continue academic instruction in both languages for years. Transitional programs use the home language as a short bridge, then move fully to English within a year or two. Length of instruction in both languages is the variable the research keeps pointing to.
Does bilingual education work for children who only speak English at home?
Yes, though the measured effects were smaller. In the Portland study, reading gains were strongest for English learners whose home language matched the program language. English-speaking families still saw benefits, just less pronounced ones.
Can tutoring replace a bilingual school program?
Not replace, but it addresses the specific gap. A randomised trial of one-to-one Spanish-language literacy tutoring found gains of roughly half a standard deviation on Spanish literacy. It did not significantly move English scores, so it supplements school rather than substituting for it.
Does being bilingual protect against dementia later in life?
The evidence here is mixed and mostly observational, which means other differences between bilingual and monolingual groups are hard to rule out. It is not a claim worth basing a schooling decision on.
How long before we see results?
Plan in years. The documented reading effects first appear around fifth grade and grow through eighth. Little happens on paper in the first few grades, which is when most families lose confidence and withdraw.
References
Borman, G. D., Borman, T. H., Park, S. J., & Houghton, S. (2020). A multisite randomized controlled trial of the effectiveness of Descubriendo la Lectura. American Educational Research Journal, 57(5), 1995–2020. https://doi.org/10.3102/0002831219890612
de Bruin, A., Treccani, B., & Della Sala, S. (2015). Cognitive advantage in bilingualism: An example of publication bias? Psychological Science, 26(1), 99–107. https://doi.org/10.1177/0956797614557866
Gunnerud, H. L., ten Braak, D., Reikerås, E. K. L., Donolato, E., & Melby-Lervåg, M. (2020). Is bilingualism related to a cognitive advantage in children? A systematic review and meta-analysis. Psychological Bulletin, 146(12), 1059–1083. https://doi.org/10.1037/bul0000301
Lehtonen, M., Soveri, A., Laine, A., Järvenpää, J., de Bruin, A., & Antfolk, J. (2018). Is bilingualism associated with enhanced executive functioning in adults? A meta-analytic review. Psychological Bulletin, 144(4), 394–425. https://doi.org/10.1037/bul0000142
Steele, J. L., Slater, R. O., Zamarro, G., Miller, T., Li, J., Burkhauser, S., & Bacon, M. (2017). Effects of dual-language immersion programs on student achievement: Evidence from lottery data. American Educational Research Journal, 54(1_suppl), 282S–306S. https://doi.org/10.3102/0002831216634463
