The National Union of Teachers could stage fresh walk-outs next term – including a series of focused regional protests – as part of a long-standing campaign against Government changes to public sector retirement funds.
It came as up to 50,000 members of the NUT – along with lecturers from the University and College Union – staged a one-day strike in London on Wednesday.
An estimated fifth of the capital’s 2,426 schools were closed by the action and around four-in-10 were partially shut.
A further 60 higher and further education colleges were also affected.
Tens of thousands of parents were forced to make alternative childcare arrangements or work from home because of the strike. At the NUT’s annual conference next month, activists will discuss plans for a proposed escalation of their action, claiming that the Government’s pension reforms will leave teachers working longer, paying more and receiving less when they retire.
It is believed they could launch a series of small-scale regional strikes in other parts of England or Wales or call for further national walk-outs.
Teachers have already staged two country-wide strikes – in June and November last year.
On Wednesday, around 6,500 union members marched through central London and held a noisy rally outside the Department for Education.
Addressing teachers, Mark Serwotka, leader of the Public and Commercial Services union, raised the prospect of a wider strike in April, with "as many unions as possible".
Christine Blower, general secretary of the NUT, said: "This protest is also a fight for state pensions. We have one of the poorest state pensions in Europe, which is a disgrace."
But Nick Gibb, the Schools Minister, said: “Strikes benefit no one. This deal is as good as it gets and takes the right balance – guaranteeing teachers one of the best pensions available but keeping a lid on rising costs for the taxpayer.
“We’ve been in serious talks for months with unions to address their concerns and reach a final settlement. This strike, ordered by the NUT’s leaders, will not get its members any further forward.”