Almost every head teacher of a state secondary school in Surrey has signed a letter to the prime minister expressing their “vehement opposition” to plans for more grammar schools in England.
The heads say this “unprecedented” coalition reflects the “confusion” caused by plans to increase selection.
They say 95% of pupils in Surrey are already at good or outstanding schools.
The government says that providing more grammar school places would give extra opportunities for poorer pupils.
The letter sent to Theresa May and Education Secretary Justine Greening says that heads in Surrey are strongly opposed to creating a “selective, segregated, two-tier state funded system of education”.
In a hard-hitting letter, they accuse ministers of creating “confusion and fragmentation” in England’s school system, with a policy based on a “nostalgic and unrealistic vision of society”.
The heads have told the prime minister that the current comprehensive system delivers high standards and that this will be put at risk by the return of a grammar system and selection by ability.
“It is impossible to have grammar schools without secondary modern schools or their equivalent,” says the joint letter from head teachers.
The head teachers say that poorer pupils are under-represented in grammars and that there is no evidence of any positive impact on social mobility.
They also call on the prime minister to focus on real problems facing schools, which they say are “continuing funding cuts, an unassuaged and escalating recruitment crisis”.
This is the latest example of head teachers exerting their collective influence – apart from the lobbying of their unions.
Every state school head teacher in West Sussex signed a joint letter to the prime minister warning that they could have to cut school hours because of a lack of funding.
The House of Commons education select committee will be carrying out an “evidence check” on Tuesday on plans to expand selection.
Committee chair, Neil Carmichael, said that since the plans for more grammars had been announced “the air has been thick with the sound of claims and counter-claims on the benefits and disadvantages of grammar schools”.
He said that it would be important for MPs to “get underneath the rhetoric and examine the evidence”.
The consultation on expanding selection will continue until next month.
A Department for Education spokeswoman said: “Grammar schools have a track record of closing the attainment gap between children on free school meals and their better-off classmates and 99% of grammar schools are rated good or outstanding.
“We want all children, whatever their background, to have access to an education that will unlock their talents. That’s why we will scrap the ban on new grammar schools and make more good school places available, to more parents, in more parts of the country.”