Headteachers in England and Wales will be balloted for strike action for the first time in a major escalation of unrest over pay.
NAHT chief Paul Whiteman said he'd "never heard more anger and despair" from members as he confirmed the union would conduct a formal ballot over pay and funding for the first time in its 125-year history.
School leaders "cannot continue to run their schools in the current circumstances", he told the TUC's annual conference in Brighton today.
The union, which has around 35,000 members, mostly in primary schools, has notified Education Secretary Kit Malthouse of plans for a formal strike ballot.
A preliminary survey of 64% of NAHT members found 84% wanted a ballot on action short of a strike if a better deal on pay and funding can't be reached.
And 55% said they wanted to be balloted on a full walkout.
It comes after the NEU, the country's largest education union, and the NAHT confirmed formal strike ballots - meaning hundreds of thousands of school staff will be asked if they want to take industrial action.
Teachers are furious at the Government's pay offer, under which experienced staff would get 5% pay hikes and newer staff see their wages rise by 8.9%.
With inflation at around 10%, unions say the offer would amount to a real terms cut to wages.
Mr Whiteman said: "I have never heard more anger and despair.
“School leaders across the country are telling me that they cannot continue to run their schools in the current circumstances.
"The neglect of pay in education and the funding to support it is now eroding the quality of education that our members can provide."
He said schools had been caught in a "vicious spiral" as insufficient pay fuels a growing staffing crisis.
Even with this year’s pay award, school leaders' pay has fallen by 24% in value since 2010, he said.
Mr Whiteman said: "They are feeling demoralised and undervalued.
"Worse than that, they are finding themselves unable to provide the level of education and support for pupils that they know is needed, due to the massive cost pressures that keep piling on to school budgets and the government’s continued under-funding of education."
The NEU confirmed on Friday that it would hold a formal strike ballot in England and Wales of around 300,000 school staff, after 86% of its teachers and 78% of support staff backed action in preliminary consultations.
The NASUWT has also said it will ballot its members in Scotland, England and Wales.
A Department for Education spokesperson said: “It is incredibly disappointing that some unions are threatening industrial action in schools.
"Strike action will damage children’s education and disrupt parents’ lives. Given the impact of the pandemic on children, it’s more important than ever that strike action is avoided.
“We have confirmed the highest pay awards for teachers in a generation – 8.9% for new teachers and 5% for experienced teachers and leaders - recognising their dedication and hard work.
