Explainer: The history of grammar schools

As the Education Secretary gives approval for a new grammar school in Sevenoaks, ITV News looks at their history and the implications for selective schooling in the future.

• What are grammar schools?

A grammar is a secondary school that selects its pupils based on academic ability, rather than factors such as geographical proximity or faith.

Pupils in their last year of primary school in certain areas take a verbal and non-verbal reasoning test called the "11-plus" to determine whether they will be able to attend.

There are 164 in England, dotted all over the country and concentrated in places like Buckinghamshire and Kent.

• How were they created?

The 1944 Education Act envisioned a three-part education system divided into secondary, grammar and technical schools. Many education authorities failed to implement the latter, so a two-tier system resulted.

• Why did they become unpopular?

Grammars were only ever aimed at the brightest 25% of the school population.

In their heyday of the 1950s and 60s, grammar schools became increasingly unpopular with the parents of those children who failed to pass the entrance exams.

Leaders decided to focus on improving education for the three quarters of the school population who were attending non-selective schools.

• When were grammar schools phased out?

From the 1960s onwards the tripartite system was largely dismantled, with grammars being closed or merged with existing comprehensives, though pockets still remain.

It was a cross-party issue - Margaret Thatcher is the Secretary of State who closed or merged the most grammars - and the Labour government then passed laws in 1998 banning the creation of new grammars.

• Who wants them back?

Boris Johnson, mayor of London, has described the decline of the grammar school system as a ''tragedy''.

Earlier this year Home Secretary Theresa May voiced support for a new grammar in her Maidenhead constituency, giving her backing to a plan to set up a school as a ''satellite'' of an existing grammar in a neighbouring borough.

Ukip's Nigel Farage has been outspoken on his desire for grammar schools to be reinstated.

• What is the situation in Sevenoaks?

Under the laws Labour passed in 1998, existing grammars are allowed to expand if there is sufficient demand.

The 450-pupil school in Sevenoaks is not covered by the ban because it is officially an annexe of Weald of Kent Grammar School in Tonbridge.

People have questioned the plans, pointing out that the two sites are miles apart.

• What are the arguments for and against grammar schools?

Campaigners argue that selective education allows for greater social mobility - allowing students who are bright but who cannot afford to pay for education to learn with others of a similar ability.

However critics have argued that grammars foster inequality. A report published in 2014 by leading university researchers found that the grammar school system widens the gap between rich and poor, with pupils who miss out on places left at an "immediate disadvantage".

Others claim that grammars are saturated with children from wealthy families.

• Will this latest decision signal the creation of new grammar schools?

That is not completely clear because although the Education Secretary said she was "satisfied" that the new annexe was not a new school in law, many critics have said exactly the opposite.

Existing grammar schools may now be able to exploit a legal loophole to build new school buildings some distance away from their main site.