Grammar schools "unequivocally damage" social mobility, according to a dossier of evidence compiled by a group of leading academics.
In a collection of essays published today by the Higher Education Policy Institute (HEPI), academics attack the "flawed" methodology in a separate HEPI paper by Iain Mansfield, a former Department for Education senior official.
Mr Mansfield's research suggested grammar schools perform well in securing places at top universities for children from less wealthy homes.
But Dr Matt Dickson and Professor Lindsey Macmillan, who wrote an essay in the latest series, question Mr Mansfield’s claim that around 45 per cent of grammar school pupils are from below median-income families.
The academics, from the University of Bath and the UCL Institute of Education respectively, say the DfE data on household income is incomplete and that “large numbers” of higher-income families are excluded, making it appear that a larger proportion of pupils in grammar schools come from poorer households than is actually the case.
Calling Mr Mansfield's methodology "flawed", they write: "Our analysis shows neither the methods nor the data used by Iain Mansfield are up to the task.
Grammar schools 'harm social mobility'
"When sounder methods and data are used, the most reliable conclusion that can be drawn is that social mobility – as measured by progression to elite higher education – is unequivocally damaged by the selective schooling system."
The essays also claim that the positive benefits for individuals attending grammar schools are outweighed by negative effects on those who do not pass the 11-plus exam.
Professors Ingrid Lunt and John Furlong, both from the University of Oxford, highlight how the attitudes to learning of many people, even in their 60s, were still coloured by whether or not they had passed the 11-plus exam, and say there are “moral concerns about the impact of selection”.
They state: “There are also moral arguments against the social segregation that is the consequence of selective secondary education… children from better-off families are over-represented in grammar schools... This, many argue, is unacceptable.
“At a time of increasing social division and inequality in England, we believe what is needed is a high-quality and comprehensive system which educates all pupils effectively, as is clearly demonstrated by countries such as Finland.”
Professor Tim Blackman, vice-chancellor of the Open University and the author of the final essay, said: “I believe we need to turn Iain Mansfield’s case for grammar schools on its head. Instead of more selection in secondary education, what is needed is less selection in higher education.
"Not only would this achieve more diverse and inclusive student communities in every university, it would also likely improve educational outcomes.”
He said that when the Open University was set up, educationally disadvantaged working-class people didn't want special treatment but instead sought access to a university for everyone. He added: "That vision has largely been realised with the OU but we are far from achieving it in the rest of the sector."
Nick Hillman, director of HEPI, said: “It is a fascinating and enduring question why, when there is such a broad consensus against grammar schools among educationalists, that they continue not only to survive but to thrive.
“As Iain [Mansfield's] paper implied, one answer could be that their existence reflects the demands of highly selective universities.”
Dr Mark Fenton, chief executive of the Grammar School Heads Association, said: "‘I am glad that the debate has started to include higher education, since grammar schools play such an important role in helping children from average and below-average income backgrounds compete on an equal footing with those whose parents can afford £35,000 in school fees.
"However, the proposition that universities should all have the same entry requirements reflects how out of touch academics can sometimes appear to be with real-life and public opinion."
A Department for Education spokesperson said: “Selective schools are some of the highest performing schools in the country. Almost all of them are rated 'good' or 'outstanding', and they are popular with parents.
“They can only receive expansion funding if they meet the high bar we have set and clearly demonstrate how they will admit more pupils from disadvantaged backgrounds.”