Heads are being urged to "vigorously" oppose the expansion of grammar schools in England.
The National Association of Head Teachers will debate calls to reject a new wave of grammars in the absence of evidence that it aids social mobility.
Its conference will hear claims Conservative plans to expand selection will only add to pressures on schools.
Prime Minister Theresa May argues grammars boost opportunities for bright but disadvantaged children.
But Labour and the Liberal Democrats oppose the move.
The NAHT argues that…