Grammar schools have been criticised for not taking in enough children from poorer backgrounds, amid reports that a number of new selective schools are being planned.
A grammar school in Tonbridge, Kent, was last week given the go-ahead to open an ''annexe'' catering to about 450 pupils at a site about seven miles away in Sevenoaks.
Since then, several other grammar schools have expressed an interest in doing the same, including in Buckinghamshire and Croydon.
Kent County Council has also said it would like to see more of its grammar schools extended to other sites, but in the meantime it has launched an inquiry into why so few children from low income backgrounds are currently attending them.
The county has 33 grammar schools - the highest number of any in the country - with 25% of secondary school age children enrolled. However just 3% of pupils at them receive free school meals, compared with 15% in its comprehensives.
Conservative councillor Jenny Whittle, who is leading the inquiry, said: "We want to really focus on why such a low proportion of children on free school meals attend grammar schools and what can be down to cut down the barriers. If they are doing well, why are they not doing the test?
"I don't believe these children are incapable of attending grammar schools, I believe there are barriers. Is it the cost of uniforms, school trips, or transport?"
She suggested bursary funds could be introduced to offset some of these costs.
"The essence of it is we believe every child should be able to attend the school that's right for them - be it a comprehensive, a special school or a grammar school," she added.
She said she hoped other grammar schools would be given the opportunity to expand if there is a demand for it.
Labour passed laws in 1998 banning the creation of new grammars - which are selective state schools - but Weald of Kent school's plan was approved because existing schools are allowed to expand if there is sufficient demand.
Wallington Country Grammar School in Surrey has now indicated it wants to open an annexe in the nearby London borough of Croydon, while Sir William Borlase's Grammar School in Marlow, Buckinghamshire, is looking into opening a satellite school.
Labour's shadow education secretary Lucy Powell said today: "Nicky Morgan will rue the day she allowed the new grammar school in Kent.
"This decision has opened the floodgates and we are now seeing moves in many selective areas to open new grammar schools.
"All the evidence shows selective education is terrible for social mobility with even Kent County Council admitting yesterday grammar schools fail disadvantaged children.
"The Government should be focusing on ensuring an excellent education for all children not just the few who get through the grammar school gates."