Researchers say the main benefit has been to make childcare cheaper for families with young children. 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.
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.
