Many parents raising bilingual or multilingual children have heard statements such as “bilingual children are smarter” or “speaking two languages improves the brain.” At the same time, others may hear warnings that two languages could confuse a child or slow development.
So what does research actually say?
The short answer is this: bilingualism can be associated with certain cognitive advantages — but these benefits are not automatic. They develop under particular conditions, and understanding these conditions helps families set realistic expectations.
This article is the first in our research-insights series, where we translate findings from bilingualism research into practical ideas for families raising children with more than one language.
A short history: From concern to opportunity
Research on bilingualism has not always been positive. Early studies in the early 20th century often suggested that bilingualism caused confusion or intellectual disadvantage. Today we know that many of these conclusions were based on flawed comparisons and biased testing methods. Later research demonstrated that bilingual children are not cognitively disadvantaged and, under certain conditions, may show advantages in specific areas such as attention control, metalinguistic awareness (understanding how language works), and flexible thinking.
Modern research, therefore, tends to view bilingualism not as a problem, but as a potential resource — one that develops through experience and use rather than through exposure alone.
What cognitive benefits are researchers talking about?
It is important to clarify what researchers mean by “cognitive benefits.” These are not general intelligence gains, nor do they mean bilingual children will automatically perform better in school.
Instead, studies have associated bilingual experience with skills such as:
- Metalinguistic awareness — understanding that words are symbols and that languages work differently.
- Selective attention — focusing on relevant information while ignoring distractions.
- Cognitive flexibility — switching between tasks or perspectives more easily.
- Awareness of multiple viewpoints, which can support empathy and perspective-taking.
Why might these develop? A bilingual child constantly manages two or more language systems. Choosing the appropriate language, switching between languages, and understanding that different people speak differently may exercise certain cognitive processes over time.
However, research is equally clear that these advantages are not universal. Human development is complex, and bilingualism is only one factor among many influencing cognitive growth.
Cummins’ Threshold Theory on language development
One of the most helpful ways to understand this complexity comes from Canadian researcher Jim Cummins and his Threshold Theory.
The idea can be explained using a simple metaphor: imagine bilingual development as a building with three floors.
The first floor: Limited language development
At this level, a child has weak skills in both languages. This situation may occur when exposure is inconsistent or when one language gradually disappears without the other becoming strong enough to replace it. A practical example could be children in highly mobile expatriate families who move frequently between countries. In such situations, a child may be exposed to several different languages over time and learn each of them to some extent, but without sufficient continuity and depth of exposure to develop strong proficiency in any one language.
Research suggests that this is not beneficial — not because bilingualism itself is harmful, but because limited language ability in general makes thinking, learning, and expressing ideas more difficult.
The second floor: One strong language
Here, a child develops age-appropriate skills in one language while the other remains weaker. This is actually very common. Many bilingual children have one dominant language depending on schooling, environment, or social use.
At this level, bilingualism is generally neutral in cognitive terms. There are no disadvantages, but the specific cognitive benefits discussed in research may not yet be evident.
The third floor: Strong skills across languages
When children develop good proficiency in two or more languages, research suggests that positive cognitive effects are more likely to emerge — particularly in areas such as metalinguistic awareness and flexible thinking.
The key message of Cummins’ Threshold Theory is therefore simple:
Bilingualism itself does not create cognitive advantages. Well-developed language skills do.
What this means in real life for families
This is where research becomes especially relevant for parents.
Many families assume that exposure alone is enough — that hearing two languages automatically produces benefits. Research suggests otherwise. Cognitive benefits are more likely when children:
- use both languages meaningfully and regularly,
- develop rich vocabulary and expressive ability in both languages
- interact socially in both languages,
- and feel emotionally secure using both languages.
In practice, this means that quality matters more than quantity. Conversations, storytelling, reading together, and meaningful interaction support language development far more than passive exposure.
It also means that bilingual development does not need to be perfectly balanced. Truly “balanced bilinguals” are rare. Most people use different languages in different contexts — one at home, another at school or work. This is normal and healthy.
A realistic perspective: Benefits without pressure
Perhaps the most important message from research is reassurance.
Bilingualism is not a competition, nor a guarantee of academic or cognitive superiority. Children do not need to become perfectly fluent in both languages to benefit from multilingual experiences. Cognitive advantages, when they appear, are gradual and emerge through long-term use.
Equally important, bilingualism brings benefits beyond cognition: identity, family connection, cultural belonging, and access to multiple communities. These are often more immediate and meaningful than measurable cognitive outcomes.
The takeaway
Research does support the idea that bilingual experience can shape how children think and process language. But the pathway is not automatic.
Cummins’ Threshold Theory reminds us that the goal is not simply raising a child with two languages, but supporting strong language development overall. When languages are nurtured, used, and valued, bilingualism becomes not just a skill, but a resource for thinking, learning, and connecting with the world.
Bilingual family core reading list
As part of our research-insights series, we are building a growing list of key readings that explain bilingualism in an accessible and evidence-based way. These sources shape current understanding of bilingual development.
1. Cummins, J. (1976). The influence of bilingualism on cognitive growth: A synthesis of research findings and explanatory hypotheses. Working Papers on Bilingualism, 9, 1-43.
Introduces Threshold Theory and explains why strong language development — rather than bilingualism alone — is linked to positive cognitive outcomes.
2. Bialystok, E., Poarch, G., Luo, L., & Craik, F. I. M. (2015). Effects of bilingualism and aging on executive function and working memory. Psychology and Aging, 29(3), 696–705.
Explores how bilingual experience may influence attention, memory, and executive control over the lifespan.
3. Blanco-Elorrieta, E., & Pylkkänen, L. (2018). Ecological validity in bilingualism research and the bilingual advantage. Trends in Cognitive Sciences, 22(12), 1117–1126.
A helpful reminder that bilingual advantages depend on real-life language use and are not universal.
4. Kovelman, I., Baker, S. A., & Petitto, L. A. (2008). Age of first bilingual language exposure as a new window into bilingual reading development. Bilingualism: Language and Cognition, 11(2), 203–223.
Shows connections between early bilingual exposure, language awareness, and reading development.