Justine Greening today stated that grammar schools would be available to:

work for everyone

In no particular order, these are current definitions of grammar schools and their innate, adamant, fundamental, irrefutable selection process precisely so they cannot be for everyone:

(in the UK) a state secondary school to which pupils are admitted on the basis of ability

originally a school teaching Latin, but more recently an academically-oriented secondary school, differentiated in recent years from less academic Secondary Modern Schools

in the UK, a school for children aged between eleven and 18 who have passed an examination that shows they are good at studying

A grammar school is a school in Britain for children aged between eleven and eighteen who have a high academic ability

British
(esp formerly) a state-maintained secondary school providing an education with an academic bias for children who are selected by the eleven-plus examination, teachers’ reports, or other means

a school in the UK for children between the ages of 11 and 18 who have passed a special examination to be allowed to go there