Children’s academic performance is not harmed if their mothers work during the first years of their lives, comprehensive research seen by The Independent shows.

A new analysis of six studies looking at 40,000 children over the past four decades has provided conclusive evidence that there is no link between mothers continuing their careers and children going on to achieve less at school, debunking a common parenting myth.

Those born in the 1970s, 80s and early 90s whose mothers worked during their early years had, on average, slightly lower literacy and numeracy scores than those whose mothers did not. However, analysis of three successive studies of children born since the mid-90s shows this disadvantage has disappeared for younger generations.

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The study’s findings will be discussed today – at the same time as Parliament debates controversial proposals to cut the ratio of childcare workers to children, a move which Labour says could reverse the progress made. Children born in 2000 or 2001 showed no significant difference in cognitive ability or behaviour at the age of five whether their mothers had gone out to work or not in their first year. Studies of previous decades showed children’s literacy and numeracy levels were around two percentage points lower when mothers worked.

The research was welcomed by parenting groups, who said it would put an end to the “emotional baggage” many mothers face when going back to work. Professor Heather Joshi, of the University of London’s Centre for Longitudinal Studies, who wrote the report, said: “There has traditionally been a concern that the employment of mothers comes at the expense of child development. But as the percentage of mothers in work has gone up, any impact on children has diminished.”

Professor Joshi said this “generational change” coincided with an expansion of childcare under the Labour government. “The most obvious thing that changed in the 90s was the New Labour government, which started taking childcare seriously as an area of public concern. In the 80s, childcare was either something that only very rich families could purchase or very poor families got offered because their child was at risk, so everyone else in the middle had to make do with informal arrangements.”

Alluding to the potential impact of the Government’s proposed changes to childcare, she added: “This wouldn’t have happened without a big expansion of childcare and if anything happens to funds available for childcare, there may be consequences.”

Children born after 2000 were the first to benefit from universal early years teaching as well as better maternity leave. More than 90 per cent of those children had some kind of formal education between three and five, compared to “around 40 or 50 per cent” in the 80s, Professor Joshi said.

The findings come ahead of a debate in the Commons today over proposals to increase the number of children looked after by each childcare worker. Last Wednesday, Nick Clegg said the changes would not go ahead – but No 10 insists no final decision has been made. Labour will table a vote in the Commons today to protect the current childcare ratios. Sharon Hodgson, shadow minister for Children and Families, said the research demonstrated the “great strides” Labour made in raising the quality of childcare. “The Government’s plans to cut the number of staff needed to look after children risk putting those improvements into reverse,” she added.

Fiona Weir, chief executive of the single-parent charity Gingerbread, said: “We welcome this research, which should put an end to some of the emotional baggage for parents who are making the decision. It’s clear that the changes in maternity leave and greater availability of childcare have played a big role in enabling parents to balance work and family. However, for single parents in particular, the crippling cost of childcare and a shortage of family-friendly jobs are making it very difficult for those who do want to return to work.”

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But Professor Joshi warned that while the evidence found no academic effects on children from mothers’ employment, this was not absolute proof of no harm being done under any circumstances. “Parents still take care about their responsibilities and should be encouraged to proceed with caution,” she said.

The research will be presented in central London today at a Campaign for Social Science event on longitudinal studies attended by David Willetts, minister for Universities and Science. On the proposed childcare reforms, a Department for Education spokeswoman said: “Parents want to be able to go out work confident in the knowledge that their children are being well looked after. Quality is central to our childcare reforms which will give parents more choice and ensure their young children have the best start in life.

“We have ensured all three- and four-year-olds can access 15 hours a week of free early education and are extending this entitlement to two-year-olds from low-income families. We are also introducing early years teachers, attracting top graduates by extending Teach First into the early years, and offering bursaries to encourage talented school-leavers into early years apprenticeships.”

Case study: My boy’s very active with his childminder

Aimee Painter, 30, and her son, Morgan, seven, from Cardiff

"It’s a relief to know that working doesn’t have any detrimental effect. Morgan was about three when I started training to go back to work. I had previously been in the pub industry and trained for the job I have now as a receptionist and administrator. His dad was never on the scene and when I made the decision to go back to work, I felt it was time to start earning and get a bit of a life.

“When Morgan was younger he went to nursery and now I drop him off at the childminder before school and pick him up there afterwards. My childminder doesn’t just sit him in front of the television; they go to the park or the library and in the holidays he goes to museums.

“I try to spend whatever time I can in the evening helping him with his reading and homework. Sometimes I do feel guilty that I’m not there to see his music assembly, or things like that, but if they’re happy at the childminder and are learning and interacting with other children, then that’s good.”