A university in Copenhagen has uncovered a troubling gap in how Denmark measures intelligence: the Wechsler Adult Intelligence Scale, the country's standard tool for assessing IQ in clinical, educational, and legal settings, significantly underestimates the abilities of bilingual young people—even those who were born in Denmark, speak fluent Danish as their primary language, and completed their entire schooling in Danish schools.
The discovery matters because intelligence tests are rarely academic exercises. They shape real decisions: whether someone receives educational support, whether they qualify for certain opportunities, whether they're placed in categories that affect their lives for years to come. A 10-point underestimation on an IQ test can shift a person from the "low average" category into "intellectual disability"—a difference that carries serious consequences.
Researchers at the University of Copenhagen tested 48 young people of Arabic-Danish background, all university students with above-average high school grades. These participants had every advantage of an equal playing field: they were born and raised in Denmark, use Danish daily, and succeeded within the Danish education system. Yet when they took the WAIS test, they performed significantly worse than expected on multiple subtests. Only their processing speed scores fell in line with what Danish peers of the same age and education level typically achieved. Linguistic tasks and visuospatial tests—interpreting visual information—dragged their overall scores down substantially.
"Our participants are young people who perform very well academically. It is therefore highly unlikely that their lower test results reflect lower intelligence," explains Ro J. Robotham, a neuropsychologist and associate professor at the Department of Psychology. "Instead, this suggests that the test does not measure equally fairly across cultural and linguistic backgrounds."
What made the findings particularly striking was where bilinguals struggled most: the Block Design subtest, which is widely considered culturally neutral because it contains no words. Yet this test turned out to be tightly connected to how strongly participants identified with their heritage culture rather than Danish mainstream culture. Working with blocks and visual patterns, it turns out, is more culturally shaped than psychologists typically assume. These skills develop not just in classrooms but through play, leisure activities, and the environments where children grow up. A test that looks objective can embed cultural assumptions that favor people from particular backgrounds.
The implication is unsettling: even tests without language can systematically underestimate intelligence in bilingual populations. The researchers found that linguistic and cultural orientation toward both heritage and Danish cultures influenced performance—a finding that challenges the assumption that fluency in the test language and successful navigation of the school system would level the field.
Ro J. Robotham emphasizes that intelligence tests themselves remain valuable tools for reducing subjective bias in psychological assessment. But they require skillful interpretation. "Psychologists should therefore be very cautious when interpreting the overall IQ score of bilingual individuals, even if they have grown up in Denmark. The results must always be considered in the context of linguistic and cultural background," she says. The University of Copenhagen is already working to strengthen its clinicians' competencies in cross-cultural testing, signaling that this research is beginning to shift practice on the ground.