Sending children to nursery at age three may not make any difference to their academic results later on.
Hundreds of millions of pounds of public money has been spent on free early years places, but new research suggests that the move has little impact on a youngster's progress in the classroom.
It concludes that, while the policy may have encouraged more mothers to go back to work, children's school outcomes were only slightly better at age five, and there was no long-term effect on their academic development.
The studies, by the Institute for Fiscal Studies (IFS) and Essex University and by Essex University and Sussex University, examined the costs and benefits of free part-time nursery places.
In 1998, the Labour government announced that all three and four-year-olds in England would be entitled to 12.5 free hours of early education a week. This has now been expanded to cover disadvantaged two-year-olds and raised to 15 hours a week.
Overall, around £800 million was spent each year on free places for three-year-olds in an attempt at a "double-dividend" of improving children's school readiness and mother's employment prospects, the researchers said.
The findings, which are being presented at the Royal Economic Society's conference in Manchester, show that between 1999 and 2007, there was a 50% increase in the proportion of three-year-olds in England benefiting from a free nursery place, rising from 37% to 88%.
The studies go on to say that overall, the increase in free places improved the results of English children at the age of five by two percentage points on average.
Children who would not have gone to nursery if they were not given a free place scored an extra 15 points on average on the early years foundation stage profile - which covers young children's development in areas such as basic literacy and numeracy.
Although there is modest evidence that free places had more impact on poorer children and those learning English as a second language, there is no evidence that it helped disadvantaged youngsters to catch up, the researchers conclude, adding that there is no evidence of educational benefit at the age of seven and 11.
The rise in three-year-olds in nursery education increased the proportion of mothers in paid work by around two percentage points.
Among those who did not also have another child under age three, there was a three percentage point increase in the numbers in jobs, and among those who started using childcare as a result of being offered free places, around one in four moved into work.
The studies contradict long-held beliefs about the long-term nursery education can have on children.
Dr Jo Blanden, of Surrey University, said: "On the face of it, our results cast some doubt over the value for money of universal early education.
"More than 80% of the children taking up free places would probably have gone to nursery anyway, and children's test scores do not seem to be any higher in the longer term as a result of the policy.
"In fact the main benefit of the policy seems to have been to make childcare cheaper for families with three-year-olds.
"It is tempting to say that the money would have been better spent on the poorest children. However, the policy's universalism may have benefits if it encourages greater take-up of provision among children from more disadvantaged backgrounds or if it mixes children from different backgrounds in the same early education settings."
Dr Kitty Stewart, of the London School of Economics and Political Science, said: "All of the expansion in free places occurred in the private sector, rather than in public nursery schools or nursery classes in primary schools.
"Children in the private sector are much less likely to be taught by qualified teachers who are best equipped to provide a high quality learning environment. This could help to explain the lack of long-term benefits."