The government is to force current grammar schools to offer lower 11-plus pass marks to children from poorer families or adopt similar “social mobility conditions” to diversify their intake, it has been reported.

According to The Times, the government will next month outline reforms to make sure grammars increase their intake of children from deprived backgrounds.

In its green paper on expanding selection, ‘Schools that work for everyone’, the government proposed that new or expanding grammar schools might have to take a proportion of pupils from lower income households.

But The Times reports that similar conditions are to be imposed on the existing 163 grammars in England.

A government source told the paper there was a “compelling” case for extending the rules to all grammar schools when a white paper setting out the plan is published in several weeks.

This will set out “social mobility conditions” that selective schools will have to meet, such as setting aside places for children from lower-income families and more flexible entry tests.

These conditions could also include encouraging many more candidates to sit entry tests, offering lower pass marks for poorer pupils and letting children sit the tests in primary schools or familiar venues near their homes.

Schools will be asked to admit some poorer children in 12-plus and 13-plus entry points, the paper reports.

“We accept that some children are late developers,” the government source said.

“They should be able to join up to the start of year 9, which is one year before they start GCSEs, and schools must help them catch up.”

Yesterday head teachers at the Association of School and College Leaders conference heckled Justine Greening over the government’s grammar school policy.

Malcolm Trobe, ASCL’s interim general secretary, told TES: “A number of the existing grammar schools are taking some interesting steps in order to ensure they have ways of ensuring a significant number of disadvantaged children”.

He mentioned the work of the King Edward VI foundation, which runs five grammars in Birmingham which reserve a set proportion of places for disadvantaged pupils.

However, Mr Trobe said the government needed to outline its “overarching strategy” in response to the green paper, rather than releasing “piecemeal bits of individual information” on its plans.

“Feeding snippets out without any detail and not presenting the overall picture is not helpful,” he said.

Peter Kent, head teacher at Lawrence Sheriff School, a boys’ grammar in Rugby,  said he was relaxed about the government introducing formal social mobility conditions for existing selective schools.

“To some extent it’s not actually a huge issue because a lot of us have been taking these measures for some time,” he told TES.

Mr Kent said his school had already taken action to “promote social mobility” by offering places 10 marks below the normal qualifying score for disadvantaged students.

A Department for Education spokeswoman said: ‎“Our proposals are about creating more choice, with more good school places for more parents in more parts of the country.

“We want to do this by lifting the ban on new grammars and harnessing the resources and expertise of universities, faith schools and independent schools.

“We have been carefully considering responses to the consultation and will respond in due course.”

Responding to the reported plans, Robert McCartney QC, Chairman of the National Grammar Schools Association (NGSA), said such “pinprick” measures to “cushion” students would further disadvantage poorer pupils in the long term, by leaving them unable to compete with more privileged students who have been coached.

“How are children from these areas going to compete in these tests against middle class children with a number of advantages from private coaching to domestic circumstances? The answer is, they’re not.

“The Government is trying to, for I think political reasons, give the impression that if they are forced to take more disadvantaged children at a lower level of entry, this would somehow be a cure. It’s at most a pinprick.”

The NGSA is instead calling for primary schools to raise their expectations of pupils, with Mr McCartney saying the “powerless” state of primary school education was the real problem for disadvantaged pupils.

“They’re perpetuating the problem of poor primary school education, by allowing for it in entry into grammar schools,” he said.

Government figures released this week revealed just 2.6 per cent of grammar school pupils were eligible for free school meals, compared with 11.6 per cent of secondary modern school pupils and 14.1 per cent of pupils across all secondary schools.