The Prime Minister said parents should not face a “lottery” when trying to find a good school place for their children.
Conservative MPs have voiced their support for grammars while also raising concerns about the funding they receive compared to other state schools.
Asked how strong a supporter he is of grammar school expansion, the Prime Minister told an event in Hove: “I strongly support the right of all good schools to expand. “I think that’s very important and that should include grammar schools.
“Under this Government, grammar schools have been able to expand and that’s all to the good.”
He added: “The principle is very clear: good schools should have the freedom to expand. Look what we’ve done with our schooling system in this country.
“We have made much more independent schools within the state sector.
“There is huge growth in academies that have more control over their admissions, more control over their finances, more control over their futures... because in the end I want for everyone in this country what I have for my three young children.
“They are at a good state primary school in London.
“It shouldn’t be a lottery, it shouldn’t be a postcode matter, it should be something that everybody gets the right to have a good school place for your children.
“The only way you can do that is to have more good schools and that is exactly what this Government’s programme has been all about.”
Once the top end of the state school system, grammar schools have been gradually phased out in recent years.