Bilingual IQ: Does Speaking Two Languages Make You Smarter?

Bilingual people do not have higher IQs on average: in a pooled analysis of 6,077 children and adults from 79 studies, bilinguals and monolinguals scored the same on nonverbal intelligence tests. The much-publicized "bilingual advantage" in mental control is very small at best, and in the largest meta-analysis of adults it disappeared after correcting for publication bias.

The reverse belief, that growing up with two languages lowers intelligence, is also wrong, and the old studies that suggested it were badly confounded. This page covers how the scientific view swung from one extreme to the other, what the best studies show about bilingual IQ and executive function, the claim that bilingualism delays dementia, and the confounds that make bilinguals hard to compare with monolinguals.

In the early twentieth century, many studies reported that bilingual children scored lower on intelligence tests than monolingual children. A 2022 paper by Ellen Bialystok and colleagues describes how much of this research was entangled with the eugenics movement. Florence Goodenough, for example, wrote in 1926 about a connection between low test scores and "the use of a foreign language in the home", in a paper the authors describe as deeply disturbing by modern standards. Most of these early studies did not control for socioeconomic status, and many relied on heavily verbal tests such as the Stanford-Binet.

In a 1946 study and a 1953 review, the researcher N. T. Darcy drew attention to a pattern: monolingual children tended to do better on verbal tests, while bilingual children did as well or better on nonverbal ones. That distinction still matters today.

The turning point was a 1962 study by Elizabeth Peal and Wallace Lambert in Montreal. They recruited 364 10-year-olds from the city's French-language schools, used language tests to sort them into monolingual and bilingual groups (164 children), and then matched a subsample of 110 children on socioeconomic status. The bilingual children scored higher on both verbal and nonverbal intelligence tests. Peal and Lambert were careful about what this meant, writing that "it is not possible to state from the present study whether the more intelligent child became bilingual or whether bilingualism aided his intellectual development".

Later researchers, including the psychologist Kenneth Paap, have argued that the selection criteria probably steered brighter children into the bilingual group. In 1960s Montreal, French speakers who also spoke English tended to come from better-off families, and the study drew on schools in both the more affluent west of the city and the poorer east. It was also the last major study of its kind, because research soon moved from intelligence tests to laboratory tasks of mental control.

The clearest answer comes from the same 2022 Bialystok paper. Her team pooled intelligence test scores that had been collected as background measures in 79 studies from her laboratory, covering 6,077 children and adults, all scored on the familiar scale with a mean of 100 and a standard deviation of 15.

• Nonverbal intelligence: there was no difference between monolinguals, less proficient bilinguals and highly proficient bilinguals, in children or adults.

• Verbal intelligence: monolinguals averaged 105.9 on English vocabulary tests and highly proficient bilinguals averaged 97.6, a gap of about 8 points. These tests measure vocabulary in English only, so they miss words a bilingual person knows only in the other language.

Paap and colleagues found the same pattern for reasoning. Across six studies of San Francisco State University students, 579 bilinguals averaged 8.53 and 488 monolinguals averaged 8.89 on a 12-item version of Raven's matrices, and none of the individual studies showed a significant difference.

The strongest design for testing whether learning a language changes intelligence comes from the Lothian Birth Cohort 1936 in Scotland. Thomas Bak, Ian Deary and colleagues studied 853 people who took an intelligence test at age 11 in 1947 and were retested in their early seventies. The 262 who had learned a second language well enough to communicate scored better in old age than their childhood IQ predicted. On a general intelligence factor, the gains were 0.19 standard deviations for those who learned before 18 and 0.32 for those who learned later, roughly 3 to 5 IQ points. Only 19 had learned their second language before age 11, the cohort was socially homogeneous, and the study was observational, so the effect may partly reflect other habits of people who choose to learn languages.

Most modern research has moved away from IQ to "executive function", the set of skills used to control attention, ignore distractions and switch between tasks. You can read more about how these skills are measured in our article on what an executive function test is. The theory is that constantly managing two languages trains these skills.

Early studies looked supportive. In 2004, Bialystok and colleagues reported that bilingual middle-aged and older adults showed smaller interference costs on the Simon task, a test of ignoring irrelevant information, and that the advantage was larger in older participants.

The evidence then weakened:

• Direct tests: in 2013, Paap and Zachary Greenberg compared bilinguals and monolinguals on 15 measures of executive processing across three studies and found no consistent bilingual advantage. The two groups also performed identically on Raven's Advanced Matrices.

• Publication bias: Angela de Bruin, Barbara Treccani and Sergio Della Sala tracked conference abstracts from 1999 to 2012 and found that studies fully supporting the advantage were the most likely to be published, while studies challenging it were published least.

• Adults: a 2018 meta-analysis by Minna Lehtonen and colleagues pooled 891 effect sizes from 152 studies. It found a very small advantage for inhibition, shifting and working memory before correction, no advantage after correcting for publication bias, and a small bilingual disadvantage in verbal fluency.

• Children: a 2020 meta-analysis by Hilde Lowell Gunnerud and colleagues, covering 143 group comparisons in children, found an overall advantage of g = 0.06, equivalent to about 1 point on an IQ-style scale. Advantages were concentrated in middle-class samples and in studies from one laboratory, and there were signs of publication bias.

The most striking claim is that bilingualism protects the aging brain. In a 2007 study of 184 patients with dementia at a memory clinic, Bialystok, Fergus Craik and Morris Freedman found that bilinguals showed symptoms of dementia about four years later than monolinguals. That study was retrospective, working back from the records of people who had already been referred to the clinic.

Prospective studies, which follow people forward in time, tell a different story. A 2017 meta-analysis by Naaheed Mukadam, Andrew Sommerlad and Gill Livingston found a combined odds ratio of dementia of 0.96 for 5,527 bilingual participants, meaning essentially no protection. The authors noted that retrospective studies are more prone to confounding by education and cultural differences in when families seek help.

A 2020 meta-analysis by John Anderson, Kornelia Hawrylewicz and John Grundy, which included both kinds of study, reported a moderate delay in the age at which Alzheimer's symptoms appear (d = 0.32) and weaker evidence of fewer cases (d = 0.10), and the authors argued that education and socioeconomic status could not explain the delay. The question remains contested. Our article on whether IQ is correlated with dementia covers how intelligence itself relates to dementia risk.

Bilingual and monolingual groups usually differ in more ways than language, which is why the results swing so much between studies.

• Socioeconomic status: in some samples bilinguals are mostly families with lower incomes, and in others mostly well-educated professionals. Either pattern can create a spurious difference in test scores, and the children's meta-analysis found bilingual advantages mainly in middle-class samples.

• Immigration and culture: many bilingual samples are also immigrant samples, so differences in schooling, health and familiarity with test formats travel with the language difference.

• Testing language: a verbal test given in a person's second language measures that language as much as reasoning. How to test bilingual children fairly is covered in our article on how bilingual children are assessed.

• Selection: people who choose to learn a language as teenagers or adults may already differ in ability, motivation or curiosity, which is why studies with childhood IQ scores, such as the Lothian cohort, matter so much.

• Definition: "bilingual" can mean anything from native fluency in two languages to school-level competence in a second one, and studies rarely use the same definition.

No. Large pooled data show no difference between bilinguals and monolinguals on nonverbal intelligence tests, and bilinguals tend to score lower on vocabulary tests given in one of their languages.

There is no good evidence that it raises IQ meaningfully. One Scottish cohort study found that people who learned a second language scored slightly better in old age than their childhood IQ predicted, but it was observational and the effect was small.

No. The early studies that suggested this ignored family background and tested children in their weaker language. Modern data show that bilingual children reason as well as monolingual children.

If one exists, it is very small. Meta-analyses find an effect close to zero in children and no effect in adults once publication bias is taken into account.

The evidence is mixed. Clinic-based studies report later onset of symptoms in bilinguals, but prospective studies that follow people over time have found little or no protection.

Speaking two languages is a valuable skill, and it does not cost children any intelligence. It also does not make anyone smarter in the way IQ tests measure, and the advantage once claimed for executive function shrank to almost nothing as better studies arrived. If you want a measure of reasoning that does not depend on vocabulary in a particular language, an online IQ test built by psychometricians is a better guide than the number of languages you speak.

1. Anderson, J. A. E., Hawrylewicz, K., & Grundy, J. G. (2020). Does bilingualism protect against dementia? A meta-analysis. Psychonomic Bulletin & Review, 27(5), 952-965. [doi.org/10.3758/s13423-020-01736-5](. doi.org

2. Bak, T. H., Nissan, J. J., Allerhand, M. M., & Deary, I. J. (2014). Does bilingualism influence cognitive aging? Annals of Neurology, 75(6), 959-963. [doi.org/10.1002/ana.24158](. doi.org

3. Bialystok, E., Craik, F. I. M., & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia, 45(2), 459-464. [doi.org/10.1016/j.neuropsychologia.2006.10.009](. doi.org

4. Bialystok, E., Craik, F. I. M., Klein, R., & Viswanathan, M. (2004). Bilingualism, aging, and cognitive control: Evidence from the Simon task. Psychology and Aging, 19(2), 290-303. [doi.org/10.1037/0882-7974.19.2.290](. doi.org

5. Bialystok, E., Hawrylewicz, K., Grundy, J. G., & Chung-Fat-Yim, A. (2022). The swerve: How childhood bilingualism changed from liability to benefit. Developmental Psychology, 58(8), 1429-1440. [doi.org/10.1037/dev0001376](. doi.org

6. de Bruin, A., Treccani, B., & Della Sala, S. (2015). Cognitive advantage in bilingualism: An example of publication bias? Psychological Science, 26(1), 99-107. [doi.org/10.1177/0956797614557866](. doi.org

7. 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. [doi.org/10.1037/bul0000301](. doi.org

8. 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. [doi.org/10.1037/bul0000142](. doi.org

9. Mukadam, N., Sommerlad, A., & Livingston, G. (2017). The relationship of bilingualism compared to monolingualism to the risk of cognitive decline or dementia: A systematic review and meta-analysis. Journal of Alzheimer's Disease, 58(1), 45-54. [doi.org/10.3233/JAD-170131](. doi.org

10. Paap, K. R., & Greenberg, Z. I. (2013). There is no coherent evidence for a bilingual advantage in executive processing. Cognitive Psychology, 66(2), 232-258. [doi.org/10.1016/j.cogpsych.2012.12.002](. doi.org

11. Paap, K. R., & Majoubi, J. (2025). Voir la vie sans rose-colored glasses. Experimental Psychology, 72(3), 115-134. [doi.org/10.1027/1618-3169/a000648](. doi.org

12. Peal, E., & Lambert, W. E. (1962). The relation of bilingualism to intelligence. Psychological Monographs: General and Applied, 76(27), 1-23. [doi.org/10.1037/h0093840](. doi.org

Hero image: Bilingual street sign in Hampstead, Quebec, by D. Benjamin Miller, CC0. Via Wikimedia Commons.