A string of government policies aimed at boosting pre-school children's educational achievement in England has had no impact, research suggests.
Three and four-year-olds are entitled to free nursery sessions
Children's vocabulary, ability to count and name shapes when they start school are no better than they were six years ago, a study of 35,000 children claims.
The Durham University research covered such policies as the expansion of free part-time nursery places.
Ministers say high quality childcare can boost children's school
Early years education has been a government priority - with £21bn invested since 1997 - and the research covered initiatives such as free nursery places for three and four-year-olds and the roll-out of Sure Start children's centres.
It also covers the introduction of the Every Child Matters policy which aims to provide more support for the welfare of children.
Researchers at Durham University's Curriculum, Evaluation and Management (CEM) Centre used a series of tests to evaluate children's vocabulary skills and their ability to do simple maths like suggesting which object is taller than the other.
They looked at how about 6,000 four and five-year-olds in 124 primary schools performed in the tests (known as Pips - performance indicators in primary school) in each of the six years of the study.
The children were asked to complete a series of fun activities by their teachers who were prompted by a computer programme.
Researcher Dr Christine Merrell said the study aimed to assess the profiles of children starting school in England "during a time of rapid change".
Taking in factors like the number of children with English as a second language and those on free school meals, it found that there was no change in the children's performance in the tests over the period 2001 to 2006.
"While the Pips assessments used in the study do not measure how many children were involved in national initiatives, one would have expected that the major government programmes would have resulted in some measurable changes in our sample of almost 35,000 children," she said.
There was also no change in the ability gap between those on free school meals and those who were not, she added.
Dr Merrell said that interpreting why such policies appeared to have no impact was beyond the scope of her research.
But she suggested that policies ought to have been better thought through and more closely monitored.
She added: "Initiatives should be based on high-quality evidence and be introduced in ways that allow for continuous scientific monitoring and adjustment in the light of evidence.
"Only then can the government really measure what does and doesn't work in education."
However, she did acknowledge that it may be too soon to assess the impact of some of the policies.
Children's Minister Beverley Hughes said: "The government has invested over £21bn on early years and childcare services since 1997 as part of an unprecedented expansion of provision for young children and families.
"Early indications are that this investment is improving outcomes for children.
"However, as the author of this report acknowledges, it is still too early to measure this with any great authority."
She said Sure Start Children¿s Centres were underpinned by research which suggested high quality, inclusive early education, leads to positive effects for children, families and communities, particularly in areas of disadvantage.
"This research also shows that two years of high quality early education can give young children a four to six month advantage at entry to reception class - and help those from poorer backgrounds to catch up."
Shadow Children's Minister Nick Gibb said there had been too many initiatives which had not been properly tested before implementation
"We need a scientific approach to education and more needs to be done to ensure the curriculum in early years in particular helps children from poorer backgrounds be ready for school in their reception year.
"Too many changes in recent years have resulted in wasted opportunities to help the most vulnerable children catch up with their more privileged peers."
Liberal Democrat children, schools and families spokesman David Laws said the report was devastating.
"The government has poured billions of pounds into early years education and it is astonishing that there is not a more detectable benefit from all of this extra cash.
"It seems that the government has failed to target money at those children most in need of support."