Theresa May’s bid to boost grammar schools was dealt another blow after a fresh study blew apart claims the selective institutions benefited schoolchildren. 

A study by the UCL Institute of Education found grammar schools had no positive impact on a teenager in terms of self-esteem, aspirations for the future or academic attainment by age 14. 

Researchers analysed data from 883 children in England and 733 children in Northern Ireland, which has a grammar school system throughout, with similar backgrounds and found little difference between the two groups. 

Critics have now called for the Government to reverse expansion of selective education. 

The Prime Minister laid out plans to create more grammar schools in the Conservative Party manifesto but was forced to scrap the divisive pledge after losing her majority at the general election. 

Earlier this month, however, education secretary Damian Hinds announced ministers would pump £50m into existing grammar schools for new places, sparking speculation that the Government was preparing to resurrect the manifesto promise. 

The new cash will be a waste of money, UCL researchers contend.

Professor John Jerrim, lead author of the study, said: “Our findings suggest that the money the Government is planning to spend on grammar school expansion is unlikely to bring benefits for young people.

“Even those children who are likely to fill these new places are unlikely to be happier, more engaged at school or have higher levels of academic achievement by the end of Year 9.”

Co-author Sam Sims added: “Schools across the country are already hard-pressed financially. Our research suggests that the Government would be better off directing their money towards areas of existing need, rather than expanding grammar schools.”

They looked at the results of tests taken in English, mathematics, verbal and non-verbal reasoning at the ages of three, five, seven and 11, as well as a vocabulary test at the age of 14, and compared results from those who went on to attend a grammar school and those who did not. 

Children were also given a series of questionnaires at the ages of 11 and 14 to gauge their thoughts on mental health, engagement at school, well-being and interaction with peers.

Josh Hillman, director of education at the Nuffield Foundation, which funded the study, said: “These findings are important because they show for the first time the impact of attending grammar schools on a wide range of outcomes, such as young people’s self-confidence, academic self-esteem and aspirations for the future.

“The evidence shows that at age 14, there is no benefit to young people of attending grammar school in these respects.

“In addition, we know from previous evidence from this study that the use of private tutoring heavily skews access to grammar schools in favour of wealthier families, dispelling the myth that they increase social mobility.

“In light of this evidence, it is increasingly difficult to understand the government’s rationale for spending money on expanding selective education rather than on improving education for all young people.”

When the grammar school funding was announced earlier this month, Education Secretary Damian Hinds said the Government wanted to “make sure every family can access a good school”.

But school leaders criticised the decision, saying they were “disappointed” that the Government was spending “scarce funding” on expanding grammars, and warned the move could be “damaging” to social mobility.

Angela Rayner, Labour’s shadow education secretary, said: “This is simply the latest evidence that the Prime Minister’s pet project of grammar school expansion will fail even on its own terms.

“Additional funding for grammar schools will do nothing to improve the outcomes of the children who attend them, but each new grammar school effectively creates new secondary moderns, a two-tier school system that robs the majority of children of the opportunities that they deserve.” 

Dr Mary Bousted, joint general secretary of the National Education Union, said: “There is not a shred of evidence that selective education provides academic benefit in the round and the negative impacts on young people in selective areas who don’t get a place in a grammar school are well documented. The Government has, once again, got its education priorities wrong.”