Signals that Theresa May is in favour of relaxing rules banning the creation of new selective grammar schools in England have provoked robust attacks from opponents of the plan. This included the government’s social mobility tsar Alan Milburn, a former minister in the Labour government that introduced the ban, who said it risked creating an “us and them divide” in the education system.

The government needs to explain how its plan to expand grammar schools would help its intended contribution to social mobility, particularly since the prime minister declared a one-nation inclusive approach to economic and social decision-making in front of Number 10 in July when she took office.

The role of grammar schools in promoting social mobility has long been a matter of ideological debate, though research has shown there is little evidence that selective schooling in England has led to improved social mobility.

While most studies have compared outcomes from the 1970s and 1980s when the number of grammar schools was in decline, our new research has analysed what happened after the most important attempt to expand grammar school education to date: the enactment of the 1944 Education Act in England and Wales.

The Act marked an attempt to move towards a level playing field for all children by introducing universally free state secondary education and preventing access to state grammar schools based on paying fees. But we found there had been no change in the relative chances of children from poorer home backgrounds either gaining grammar school places or obtaining formal school qualifications.

What changed in 1944

The 1944 Act was the culmination of long-term aspirations of Boards of Education in England and Wales to open secondary educational opportunities to all social classes on equal terms.

For decades prior to 1944, grammar schools had already formed an important part of secondary education, but there were significant structural impediments to achieving strong social mobility. Many grammar school places were offered non-competitively on a fee-paying basis. Free grammar school places were allocated on the basis of performance in a competitive 11+ exam, open to children from all backgrounds. But, in the 1920s, only about a third of children won free places, many from better-off families. This rose to about half by the early 1930s.

By the end of the 1930s, boys with fathers in managerial or professional occupations were more than four times more likely to gain grammar school entry compared to boys from skilled manual families – and girls were three times more likely. Compared to children from semi-skilled or unskilled households, the top social groups were five to six times more likely to gain entry.

After the Act, rather than their parents paying for a place, pupils were admitted to a selective grammar or technical school only if they performed well in an 11+ exam, taken by all children at the end of junior school. Those who failed to make the grade were sent to a new type of non-selective school, known as a secondary modern.

Access did not get fairer

Our research examined whether or not the 1944 Act made a difference to children who would have been disadvantaged in the earlier era because their parents would be unlikely to be able to pay the required secondary school fees. We compared the chances of gaining a grammar school place among boys and girls with managerial or professional fathers compared to those with skilled manual or skilled non-manual fathers or with semi-skilled or unskilled fathers.

We found no evidence of change among these socio-economic groups in the 20 years following the Act compared with the 20 years prior to it. In other words, there was no improvement in social mobility. This was also the case when we looked at family qualifications. Children from families with at least one parent who had qualifications retained a big comparative advantage in gaining a grammar school place after the Act came into force.

We also examined the relative chance of children achieving formal school qualifications. Both in the early part of the 20th century and after the 1944 Act, grammar schools offered nationally recognised exam qualifications at the ages of 16 and 17-18. For the great majority of children who attended non-selective education, there was virtually no chance of obtaining these qualifications because they typically left school before then. The minimum leaving age was 14 before the Act and it rose to 15 in 1947. Again, we found that the chances of children from poorer home backgrounds gaining schools qualifications was unaltered post-1944 compared to pre-1944.

One possible exception was some evidence of a slight improvement in the number of boys with unskilled fathers who achieved formal school qualifications. But it is hard to pin this down to the 1944 Act alone as our data suggest that the gains were starting to appear for cohorts just before the Act was introduced.

Why it did not boost social mobility

Leading observers in the 1950s noted that poorer working class families were worried that their children would have to forego earnings if they remained longer in secondary education. They were also worried about inadequate maintenance grants. Also, some families did not want their children to enter the sort of occupations typically linked to grammar school attendance, for example banking or teaching.

By contrast, parents in professional or supervisory occupations were more likely to express preferences for grammar school education, a longer stay at secondary school and the need for further education after school.

There was also an emerging view among sociologists in the 1950s and 1960s that the use of IQ testing in the 11+ exam – with a large emphasis on areas such as the use of language, correct grammar and sentence logic – tended to benefit families with relatively highly educated parents. By 1965, the Labour government shifted education policy, moving away from selective grammar schools to a generally more non-selective secondary school system: comprehensives. Given a failure to improve educational prospects among children from less well-off home backgrounds, this switch in emphasis was unsurprising.

Although grammar schools still exist in some pockets of the country such as Kent and Buckinghamshire, in 1998, Tony Blair’s Labour government introduced a law prohibiting the expansion of new grammar schools.

If grammar school education is once again to be expanded, then the onus falls on government to clearly spell out why today’s climate offers improved opportunities across all households and how the selection process can guarantee more opportunity to the less well off.