Sending three year old children to nursery may not make any difference to their academic results later on, suggest researchers.
£800m has been spent annually on free places for three-year-olds since 1998.
Researchers say the main benefit has been to make childcare cheaper for families with young children.
They conclude that while the policy may have encouraged more mothers to return to work, there was no long term effect on children's academic development.
The studies were carried out by the Institute for Fiscal Studies (IFS) and Essex and Sussex universities.
Since 1998 all three and four-year-olds in England have been 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.
The hope was to achieve a "double-dividend" - improving children's school readiness and their mothers' employment prospects, the researchers said.
The studies 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 policy lead to a 2% increase in the proportion of mothers in paid work, the researchers found.
Among those who did not also have another child under the age of three, there was a 3% increase in the numbers in jobs.
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.
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,
They also found no evidence of educational benefit at the age of seven and at 11.
Jo Blanden, of Surrey University, said that "on the face of it", the results seemed to question whether the policy had proved to be value for money.
"More than 80% of the children taking up free places would probably have gone to nursery anyway," she said. "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."