A private tutoring tax could help poorer children in Kent get into grammar schools, according to research showing that less well-off families were less likely to secure places.

The idea of a tax follows research that indicated high-income families are much more likely to use private tutors to prepare their child for the grammar school entrance test than low-income families.

A study by Professor John Jerrim of the UCL Institute of Education revealed children who receive private tutoring are five times more likely to get into grammar schools than those who do not get extra help.

The study investigated 1,800 children from areas of England which still have grammars, including Kent. It found that 70% of those who received tutoring got a place, compared to just 14% of those who did not get help.

Professor Jerim said one way of levelling the playing field would be to introduce a voucher system for less well-off families to pay for tuition.

“The government claims that expanding grammars will boost social mobility. But our research shows that private tuition used by high-income families gives them a big advantage in getting in.”

“The government therefore needs to explain how they are going to level the playing field between different income groups.”

The government has recently indicated that it might be prepared to allow grammar schools to expand although a pledge to create new ones has fallen by the wayside following the general election in 2017.

The culture of private tutoring is a well-known phenomenon in Kent, with a flourishing market in private tuition centres.

“The government claims that expanding grammars will boost social mobility. But our research shows that private tuition used by high-income families gives them a big advantage in getting in” - Professor John Jerim

Kent County Council has attempted to neutralise the advantages of private tuition, by introducing a new exam that is less easy to coach for.

It has also carried out its own investigation into how to improve social mobility in grammar schools.

That has seen some of the county’s highest performing selective schools introduce a policy of admitting small numbers of children who have passed the test but with lower scores.

Anti-selection campaigners said the findings showed the current test was flawed.

Dr Alan Bainbridge from KEN (Kent Education Network) said: "This research proves what we've all suspected - expensive private tuition works.

"The idea that the Kent Test is a true test of ability is nonsense, children practising maths and English with skilled tutors clearly have more chance of passing than those without any help.”

“Kent will have a new 11-plus test in 2019 and we want the council to acknowledge the huge tuition problem and do something about it. Prep schools and test tutors are effectively rigging results for wealthy families.”