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Earlier work has repeatedly linked more schooling with lower dementia risk, but it has not been possible to separate other factors to isolate the impact of education alone.
A single-day cutoff in the summer of 1957 quietly split a generation of British schoolchildren into two groups.
The children born before September 1, 1957, could leave the classroom at 15. Those born a day later had to stay until 16, under the Raising of School-Leaving Age Act that took effect in 1972 across England, Scotland, and Wales.
Nearly half a century later, researchers have used that calendar line to settle a question that correlation studies have never been able to answer.
A study published on October 23, 2026, in Proceedings of the National Academy of Sciences finds that the one extra year of compulsory schooling produced a measurable reduction in Alzheimer’s disease and related dementias in the cohort decades later.
The authors, led by economists at the USC Schaeffer Institute and the University of Wisconsin-Madison, describe the result as the first causal evidence that education itself lowers dementia risk, rather than merely tracking it.
Earlier work had repeatedly linked more schooling with lower dementia risk, but researchers could not separate education from income, health habits, or family background.
“By taking advantage of this school reform, we can separate the effect of education from many of the other factors that differ across people,” lead author Silvia Barcellos said in the USC announcement.
A natural experiment, not another correlation
The researchers exploited what economists call a regression discontinuity.
Two children born days apart, one in late August 1957 and one in early September, faced sharply different schooling requirements but were otherwise statistically indistinguishable.
By comparing the two groups through UK Biobank hospital records, death registries, and self-reported medical histories, the team isolated the effect of that extra year.
The reform itself raised the share of students staying in school through age 16 by 14 percentage points, according to the USC announcement. The subset who stayed on because of the policy went on to show lower rates of ADRD than their peers born just before the cutoff.
Genes do not have the last word
The most striking finding concerns people already at high inherited risk. The team built a polygenic index capturing genetic susceptibility to Alzheimer’s and then compared outcomes across risk groups.
Additional schooling reduced dementia incidence even among participants with the highest genetic risk, narrowing the gap between high and low genetic-risk groups in the research team’s earlier working paper on the same data.
“Genes help shape disease risk, but they do not necessarily determine the outcome,” coauthor Leandro Carvalho said in the USC announcement.
What it means for an aging US population
An estimated 7.4 million Americans age 65 and older are living with Alzheimer’s, according to the Alzheimer’s Association’s 2026 Facts and Figures report, which also finds that about 1 in 9 people in that age group has clinical Alzheimer’s dementia.
The 1957 cohort is only now entering the age at which dementia typically appears, so additional data will accumulate as the group ages. The authors caution that their estimates reflect one extra year of schooling at the end of compulsory education, in a specific country and era, and may not generalize directly to policy changes elsewhere.
