The Government should scrap the 11-plus test to determine which children go to grammar schools – or force all pupils to take it – if it wants to improve social mobility, according to one of the Department for Education’s main champions for new schools.

Toby Young, the director of the New Schools Network (NSN), which plays a key role in delivering free schools and grammars, said the decision for which children go to grammar schools could be handed over to primary headteachers. Simply letting existing selective schools replicate themselves as they are will do nothing to improve social mobility, he added.

Speaking exclusively to The Independent, Mr Young said he believed “no more than five” grammar schools would open by the end of the current Government.

Asked if that was five schools too many, he said: “Wearing my NSN hat, no comment.” But made clear his personal view was that there was “no strong case for opening new grammars in areas already served by good state comprehensives”.

While school groups will be encouraged to open the selective schools in disadvantaged areas, Mr Young said “there may be one or two exceptions”, and did not rule out the possibility of grammars opening in affluent areas of the country.

His comments follow an announcement in the spring Budget on Wednesday that a further £320m is to be set aside for the opening of around 140 new free schools – some of which will be grammars - should the Government get the green light to lift the current ban on their expansion.

Defending the plans, Prime Minister Theresa May has argued that grammar schools can improve the prospects of children from poorer backgrounds and their expansion will help end the current “selection by stealth” system within state comprehensive schools.

The move comes amid fierce resistance from campaigners, however, and follows the publication of a number of scathing reports detailing both the financial and potential social costs of free schools, which are independent of local authority.

Grammar schools in particular have been contested by social mobility groups such as the Sutton Trust, which insists the enforced segregation of children of different abilities only widens the gap between rich and poor pupils.

Pisa rankings 2015: The best countries in the world for education Show all 20 1 /20 Pisa rankings 2015: The best countries in the world for education Pisa rankings 2015: The best countries in the world for education Singapore Singapore was the top performing country across all three subjects (maths, science and reading) in the 2015 PISA tables. The small Asian country is renowned for its high academic standards and produces excellent results, particularly in mathematics. Pupils here learn maths by what is known as the “mastery method,” which teaches children how to solve problems as a class and errs away from more traditional recitations of formulae. Singapore selects its teachers from the top 5 per cent of graduates, and teachers are very highly regarded as societal influencers. Getty Pisa rankings 2015: The best countries in the world for education Japan Japanese schools came in 2nd for Science, 5th in the world for maths and 8th for reading skills. Japan has one of the best-education populations, with zero illiteracy recorded and strong emphasis on arithmetic and geography. While children around the world typically learn between 26 and 33 letters of the alphabet, Japanese pupils will know 1,006 kanji characters by the time they leave primary school. Getty Pisa rankings 2015: The best countries in the world for education Estonia Dubbed the “new Finland” by some, Estonia has risen rapidly towards the top of the Pisa rankings despite being one of the world’s youngest countries. Estonia spends around 4 per cent of GDP on education. Getty Pisa rankings 2015: The best countries in the world for education Taipei Taiwan has been known as a centre for technical excellence for decades and its students perform consistently well in technology, maths and sciences. Education is compulsory from age six, and some 95 per cent of all students continue their education after age 15. Getty Pisa rankings 2015: The best countries in the world for education Finland Children in Finland don’t start school under age seven, yet consistently produce some of the best results in the world. The country’s education system has a somewhat alternative approach to that of most OECD countries, placing emphasis on playtime and creative learning. Pupils don’t sit tests until they reach 16. Getty Pisa rankings 2015: The best countries in the world for education Macau Most schools in Macau are private or subsidized. There are only a handful of government or state schools, which tend to teach in Portuguese or have a strong emphasis on pupils learning the language. The majority of schools are also selective grammar schools which focus heavily on languages, mathematics and sciences over vocational subjects. Getty Pisa rankings 2015: The best countries in the world for education Hong Kong A former UK colony, Hong Kong education has been closely modelled on the British system in the past,. Education is free and compulsory in primary and junior secondary schools. Independent schools follow the International Baccalaureate, UK or US curricula. The territory participates separately from China (Shanghai, Beijing, Jiangsu, Guangdong) in the Pisa league tables. Rex Pisa rankings 2015: The best countries in the world for education South Korea South Korea has long been one of the world’s top academic achievers, but at the price of very long school days for students. Many start school by 8am, and carry on until late at night at private study clubs. Getty Pisa rankings 2015: The best countries in the world for education New Zealand While the New Zealand school curriculum is not dissimilar to the UK’s, children here are not required to start school until age six. The country also has eight state-funded universities offering degrees in a range of subjects. Getty Pisa rankings 2015: The best countries in the world for education China Getty Pisa rankings 2015: The best countries in the world for education Slovenia Slovenia scored highly in this year’s maths and science results. Basic education for children ages six to 15 is compulsory and free for children in Slovenia. International citizens are taught the Slovenian language at the beginning of school. Rex Pisa rankings 2015: The best countries in the world for education Australia Australian Pisa candidates came in 14th place for Science, 15th place for reading and 23rd place for Maths – slipping down in the ranks on previous years. Australia has the third highest number of international students in the world behind the UK and US, despite having a much lower population overall. The school system is split mainly into government state-funded schools, Catholic faith schools and independent fee-paying schools. Getty Pisa rankings 2015: The best countries in the world for education United Kingdom The UK jumped to 15th place for science in this year’s Pisa tables, up from 21st in 2012. According to the report, teachers in the UK are among the youngest across all developed countries. The total amount spent on British education exceeds that of most other participating countries – and critics argue the education system should provide better results because of this. Getty Pisa rankings 2015: The best countries in the world for education Germany Schooling in Germany is governed by individual states, which each have their own education departments and policies. Normally, children begin primary school at age six but secondary school options vary widely. Germany increased its expenditure on educational institutions from primary to post-secondary non-tertiary levels, despite declining enrolments, and teachers have competitive salaries compared to others as a result. Getty Pisa rankings 2015: The best countries in the world for education Netherlands Dutch children were found to be the happiest in the world in a 2013 Unicef study. Schools typically don't give much homework until secondary level and students report little pressure and stress. Rex Pisa rankings 2015: The best countries in the world for education Switzerland Just five per cent of children attend private schools in Switzerland. Lessons are taught in different languages depending on the region of Switzerland, with German, French or Italian the most common languages of instruction. From secondary onwards students are separated by ability. Rex Pisa rankings 2015: The best countries in the world for education Ireland The majority of secondary schools in Ireland are privately owned and managed but state-funded, but there are also state comprehensives and vocational schools. The country performed especially well in Pisa reading tests - coming in fifth place globally. Rex Pisa rankings 2015: The best countries in the world for education Belgium Belgian schools came in 15th place for science in this year’s Pisa table. Schools here are free, and regulated and financed by three separate communities – Flemish, French and German-speaking. Boys in Belgium perform significantly better than girls in school according the latest OECD reports. Rex Pisa rankings 2015: The best countries in the world for education Vietnam Education in Vietnam is state run system of public and private schools. The country took part in the Pisa tests for the first time in 2012 and scored higher in reading, maths and science than the UK and US. This is believed to be partly a result of high spending levels on education and hardworking culture instilled in children from a young age. Getty Pisa rankings 2015: The best countries in the world for education Canada Education is compulsory up the age of 16 in most Canadian provinces, apart from Manitoba, Ontario and New Brunswick where pupils must stay on until 18 or when high school diploma is achieved. The education system varies between French and English-speaking provinces. Rex

It is, according to Mr Young, a “problem that is going to be addressed” as plans are drawn up between the Department for Education and NSN for expansion.

“Exactly what form that takes I don’t know, but it could be a national test as opposed to a test devised by a school or a local authority,” he said. “It could be a test that doesn’t include any general knowledge questions, just progressive matrices and verbal reasoning.

“It could be for all children to take at the end of primary school – or we could do away with the test altogether and ask primaries to nominate [top-performing children],” he said. “Back in the grammar school heyday that is how some grammar schools admitted children – they just went on headteachers’ recommendations.”

The difficulty with trying to create a “tutor-proof test”, he added, is that it is in the very nature of tests that children can practice and get better – particularly for a child born into a supportive, aspirational middle-class family.

In his new role as director of the New Schools Network, the journalist turned educationalist has been careful to ensure his professional views are non-partisan.

Speaking in a personal capacity, however, Mr Young – himself a grammar-school alumus – admits his own opinions on selective schooling continue to waver.

He said he had no issue with faith schools and felt positively about selection by aptitude – arguing parents wanted “choice” and the creation of specialist schools from maths academies to Brit School equivalents would be put forward for new school openings.

On grammar schools, however, he was less confident: “The truth is I’ve come down on both sides of the fence and I feel really conflicted about it,” he said. “At the moment certainly most of the beneficiaries [of grammar schools] are for middle-class children like I was.

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“If you just let existing grammars replicate themselves then it doesn’t seem likely they’ll have a huge impact on social mobility, because they don’t admit enough children from disadvantaged backgrounds.

However, he said he didn’t believe this alone was a “knock-down argument” against opening more grammars, “because there are things you can do to incentivise them to admit more children from less privileged backgrounds”.

There are currently 163 grammar schools in England with a total of 167,000 pupils. These pupils, according to Government figures, are much less likely to have special education needs or be eligible for free school meals that average.

Grammar schools also have a slightly higher than average proportion of non-white pupils.

Should the Government succeed in getting the ban lifted, one of the ways in which NSN hopes to be working with grammars is to set up feeder primary schools within disadvantaged communities, which could offer coaching in preparation for such a national test.

“One of the reasons I’ve said in the past that grammars haven’t done much for social mobility is that the percentage of children getting into grammars on free school meals is so low,” he added.

“In fact, the proportion of children being offered places at grammars from independent prep schools is higher than that of children on free school meals.

“You can do stuff about that – you could say to a proposer group, ‘You’ll only be allowed to open this grammar school if you accept more than the local authority average of children on free school meals’.”

In an ideal world, Mr Young said, he would create a system that ensured selective schools take more than the average number of children on free school meals – a common indicator of poverty – than the local authority average.

Proposer groups – which can be independent parties of parents, educators, charities or businesses – would be encouraged to open schools in areas of need and have systems in place to encourage diversity. However, he said it was “unlikely” the DfE would mandate this.

Lifting the ban would also make “partial selection” possible – a model he admires and hopes to develop – whereby a small percentage of each year group is selected for a flexible “grammar stream” according to their performance levels.

There are examples of high-performing partially selective schools already in place – Ashlawn School in Rugby, for example, selects 12 per cent of each year group depending on their performance in the Warwickshire 11-plus.

The remainder of each year group is mixed ability, creating a grammar stream which children can move in and out of as their grades fluctuate.

“It might create an incentive for children to work harder,” said Mr Young, “but the really attractive thing about that model is that you get the more able children helping to pull some of the other children up.

“One of the arguments against grammars is that by creaming off the most able children, those pupils are no longer there to have a positive impact on their peers.

“The thing about partially selective schools is that you get this movement in and out of the grammar stream and it means you are not herding children into sheep and goats at age 11, because the sorting process is fluid up until GCSEs.”

The idea of any selection within education is one that sits badly with comprehensive advocates. But Mr Young, who was co-founder of the country’s first free school in west London, is no stranger to criticism.

His appointment as NSN director was attacked as a “PR gimmick” by shadow Education Secretary Angela Rayner, who has reportedly refused to engage with him in debate on air.

He is unapologetically outspoken on Twitter, adding that he has “had to think a littler harder” about his tweets before starting the new job. “I have to put my phone down before 9pm,” he said.

In defence of free schools, however, he remained clear: “Most people imagine them as whacky and progressive in which children can do whatever they like and the teachers have no authority, but this is simply not the case.

“The truth of the matter is the Government needs to create more school places, and free schools are proven to be the less expensive way forward.”

Mr Young's comments came as it emerged the Government is looking at a major shakeup of the 11-plus that would see grammar schools forced to accept lower pass marks for poorer pupils.