Sometime in the mid-2010s, something that had held steady for nearly a century quietly went into reverse.

For generations, researchers had observed a reliable pattern: people scored higher on IQ tests than their parents had. The gains were substantial — roughly three points per decade across most of the 20th century — and they showed up across countries, income levels, and demographics. Researchers called it the Flynn Effect, after political scientist James Flynn, who documented and popularized the phenomenon.

Then it stopped. And in several countries, it reversed.

Sources: Bratsberg & Rogeberg (PNAS, 2018); OECD PISA 2022 Results

What the Flynn Effect actually was

Before we talk about the reversal, it helps to understand what was actually being measured. IQ tests do not measure some fixed, innate quantity of human intelligence. They measure specific cognitive skills — abstract reasoning, pattern recognition, processing speed, working memory — and those skills are heavily shaped by environment.

James Flynn himself was careful about this. The gains his data revealed were not evidence that people were becoming smarter in some broad, essential sense. They were evidence that the modern world — with its longer schooling, more cognitively demanding work, richer abstract media — was systematically training certain kinds of thinking.

Which leads directly to the most important implication of the reversal: if the gains were environmental, so is the decline.

The reversal — what the research actually found

The landmark study came from Norwegian researchers Bernt Bratsberg and Ole Rogeberg, published in the Proceedings of the National Academy of Sciences in 2018. Using decades of military conscription data — IQ scores for nearly every Norwegian man of conscription age — they found that scores rose steadily for decades and then began declining among cohorts born after the mid-1970s.

The most significant part of their finding was not the reversal itself. It was where they found it. The decline appeared within families — meaning younger brothers scored lower than older brothers, ruling out the genetic and demographic explanations that skeptics immediately reached for. This was not a story about which families were having more children. It was a story about something changing in the environment that all of these children shared.

Similar patterns have since been documented in the United States, Denmark, France, the Netherlands, and Finland — though with important variations by country and by the specific cognitive domains being measured.

The PISA data and what it adds

IQ trends are one data source. International academic achievement tests are another, and in 2022 they delivered the most alarming single-cycle result in the history of the Programme for International Student Assessment.

Between 2018 and 2022, average math scores across OECD countries fell by approximately 15 points — the equivalent of roughly three-quarters of a school year of learning, lost in a single four-year cycle. Reading scores fell too. The OECD, which administers the test, was direct: this was unprecedented.

The COVID-19 pandemic accounts for a significant portion of this decline — school closures, remote learning, and psychological disruption all exacted measurable costs. But researchers note that some concerning trends predated the pandemic, and that the countries which maintained or improved their scores during this period share certain characteristics in their education systems that go beyond simply "staying open."

What is driving the reversal

The leading explanations

Researchers have proposed several environmental drivers, none of which is considered sufficient on its own. Changes in educational practice — particularly away from rote memorization and toward less structured learning — appear in several analyses. Nutritional factors, including iodine deficiency in some populations, account for part of the decline in specific regions. Income inequality and differential access to cognitively stimulating environments have widened in many countries over the same period.

And then there is the digital environment. Neuroscientist Jared Cooney Horvath, in written testimony before the U.S. Senate Committee on Commerce, Science, and Transportation in early 2026, argued that Gen Z may be the first modern generation to score lower than the previous one across standardized cognitive measures — and attributed this significantly to the design of digital learning environments and the cognitive habits cultivated by short-form content consumption.

His argument, simplified: the skills that the Flynn Effect rewarded — sustained abstract reasoning, reading complex texts, holding multiple ideas in working memory — are precisely the skills that scroll-optimized digital environments train against.

What it means — and what it does not

Here is what the research does not support: the claim that younger generations are innately, permanently, or globally less intelligent than their parents. The data is geographically uneven — some countries and education systems have maintained or improved their results. The declines are concentrated in specific cognitive domains, not uniform across all measures of thinking. And the within-family evidence from Norway makes the genetic explanation untenable.

Here is what it does support: the cognitive environment — the sum of what a child reads, watches, practices, and is asked to do over years of development — shapes measurable cognitive capacity. That environment has changed significantly in ways that appear to be working against the development of certain deep cognitive skills. And because the causes are environmental, they are in principle addressable.

The question is what addressing them actually looks like — at the level of policy, of schools, and of individual families making decisions about how their children spend their attention.

We will be writing about all of it.

Raising Sharp publishes twice a month on cognitive development, attention, and education. Subscribe above to receive new pieces when they publish. One resource we occasionally point readers toward: The Directorate, a monthly mission-based newsletter that builds math, reading, and critical thinking skills in a spy-story format — designed precisely for the kind of sustained, engaged practice this research points toward.