By 
On the morning of Monday, June 1, 1932, classrooms across Scotland went quiet. Almost every child born in 1921 sat down with the same paper, the same instructions and the same time limit. In all, 87,498 children took part.
Then the results were filed away and largely forgotten. More than 60 years later, they became one of the most valuable datasets in the science of how minds age.
A whole country takes a test
The project was the Scottish Mental Survey of 1932, run by the Scottish Council for Research in Education. The children took the Moray House Test, a 45-minute paper with questions on vocabulary, reasoning, arithmetic and spatial skills.
Scotland ran a second survey on June 4, 1947, testing more than 70,000 children born in 1936. No other country has tested the intelligence of nearly an entire birth year, let alone done it twice. But once the original goals of the surveys were met, the records sat unused for decades.
Rediscovering the ledgers
In 1997, Edinburgh psychologist Ian Deary and his colleague Lawrence Whalley, a psychiatrist at the University of Aberdeen, rediscovered the survey data. The handwritten records had been kept in a University of Edinburgh building rented by the education council.
The researchers realized what they had. Here were childhood test scores, taken under identical conditions, for an entire generation who were now in their 70s. If they could find the survivors and test them again, they could see how well childhood ability predicted thinking skills in old age.
Whalley led early follow-ups in Aberdeen. Then, starting in 1999, Deary and the late geriatrician John Starr began tracing people in and around Edinburgh. They hoped to recruit 500. In the end, 550 people born in 1921 agreed to take part, forming the Lothian Birth Cohort 1921.
The same test, 68 years later
At an average age of 79, the volunteers sat down and took the very same Moray House Test they had taken as 11-year-olds. For many, it was a strange experience, revisiting the exact questions they’d answered as children in the 1930s.
The results were striking. Scores at age 11 and age 79 were strongly linked, with a correlation of about 0.66. In plain terms, childhood test scores accounted for roughly 40 to 50 percent of the differences in thinking skills between people in their late 70s. Children who scored well in 1932 tended to still score well as older adults.
That’s a remarkable amount of stability across almost seven decades, a period that for this generation included the Great Depression, World War II, careers, families and the many health changes of later life.
What childhood scores didn’t predict
There was an important twist. When the Lothian group was retested at 83, 87 and 90, childhood scores predicted where people started in old age, but they didn’t predict how quickly their thinking declined after 79.
In other words, a high-scoring child tended to become a sharper older adult, but wasn’t protected from the decline that comes with aging. The other half of the picture, how fast minds slow down, seemed to depend on other factors, such as health, lifestyle, genetics and brain changes like shrinkage in the hippocampus or the onset of conditions like Alzheimer’s disease.
That’s partly why the cohorts became so valuable. Because researchers had a childhood baseline, they could test whether factors linked to sharper thinking in old age were genuine benefits or just reflected who was already sharper as a child. In some cases, the apparent benefit largely disappeared once childhood scores were taken into account.
Beyond thinking skills
The Scottish data turned up other surprises. In a 2001 study published in the BMJ, Whalley and Deary tracked all 2,792 Aberdeen children who took the 1932 test. They found that a 15-point disadvantage in childhood test scores was linked to a lower chance of still being alive at age 76.
The reasons are still debated. Childhood test scores may reflect early health, nutrition and family circumstances, and they’re also linked to later education, jobs and health decisions. The researchers have stressed that these are patterns across large groups, not predictions about any one person’s life.
A legacy still being studied
The 1921 group was tested individually every few years until about age 92, and researchers continued tracking their health afterwards. A second group, the Lothian Birth Cohort 1936, recruited 1,091 participants from the 1947 survey and added brain scans, blood tests and genetic data.
Together, the two cohorts have produced hundreds of studies on how thinking skills change from childhood to old age. And it all goes back to a single Monday morning in 1932, when tens of thousands of Scottish children picked up their pencils for a test they would never imagine taking again.
