The time spent in education impacts of mental ability later on.
The raising of the school leaving age to 15 over 50 years ago could go some way to reducing dementia rates in the elderly, a study has suggested.
A Cambridge University team compared the mental abilities of elderly people, and found those born after the change fared better.
They say that further changes to the school leaving age could improve mental abilities and curb dementia rates more.
Experts said more information on how education affected dementia was needed.
Around 700,000 people in the UK currently have dementia. Experts have estimated that by 2051, the number could stand at 1.7m.
In this study, researchers compared a group of over 9,000 people aged over 65 tested in 1991 with over 5,000 over-65s tested in 2002
They were all given a standard test used to detect early signs of dementia, which involves naming as many animals as possible within a minute.
The researchers identified a small but potentially significant increase in the number of words a minute people used in the later group.
Poor cognitive function is known to be linked to developing dementia, and it is already known that dementia is less likely in people who been educated for longer.
Previous research has shown that education is beneficial because it increases the number of neural connections in the brain.
The school leaving age was set at 15 in 1947, rising to 16 in 1972. The government announced two years ago that, by 2015, teenagers would have to stay in education or training until they were 18.
Writing in the journal Aging, Neuropsychology and Cognition, the researchers say "The increase in educational levels that we observed is consistent with changes in the mandatory school leaving age in England."
Other factors including fewer heart attacks, increased prescription of drugs to reduce high blood pressure, fewer people smoking and improvements in early life nutrition are also likely to have had an effect on the cognitive abilities of the 2002 group.
- full-time education compulsory for children aged five to 14
- leaving age raised to 15
- leaving age goes up to 16
- teenagers will have to stay in education or training until they are 18
Dr David Llewellyn, who led the study, said: "Dementia happens when people decline cognitively to the point where it interferes with their ability to do basic things like cook.
"It tends to happen later in life, but the changes that lead to it tend to start much earlier.
"These findings are important because they affect our projection of what's likely to happen in the future.
"It's not going to prevent what is essentially an epidemic of dementia, but it may mean it might not be quite as bad as we have predicted."
Dr Llewellyn said changes to the school leaving age after the period covered in the study would should also lead to improvements in cognitive abilities, and therefore mitigate dementia rates.
And he added: "When talking about what we should do in terms of education and changes to the school leaving age, this kind of study should feed into it."
But Neil Hunt, chief executive of the Alzheimer's Society said: "Whilst we have a lot of really good evidence on healthy lifestyles and the fact that they can decrease risk of dementia, there isn't enough evidence on education and dementia to draw any conclusions.
"We know conditions such as diabetes and obesity are on the rise and that they increase people's risk of dementia - unfortunately this may have the opposite effect. "