PUPILS across Essex were facing disruption to lessons today as teachers joined rallies, marches and picket lines to protest against changes to their pay, pensions and working conditions.
The one-day walkout, called by the National Union of Teachers (NUT) - one of the biggest teaching unions - is the latest move in its continuing campaign of industrial action.
Union leaders said the early indications were that the strike was well-supported.
The action has been condemned by the Department for Education which says that it will disrupt parents' lives and damage children's education.
NUT general secretary Christine Blower said: "Certainly the message we are getting is that the action is well-supported. On the back of the 60-hour week workload diary survey teachers are just feeling overwhelmed."
She said rallies and marches are taking place all over the country and that "people will be out and about".
Ms Blower said the NUT has been staging events around the country on a weekly basis for some time to tell the public about their campaign and the issues they are highlighting.
"We are saying that very bad things are happening to education and (Education Secretary) Michael Gove needs to listen."
The NUT's bitter dispute with the Government focuses on three issues - changes to pay, pensions and workload.
The walkout could affect thousands of schools across the two nations, and force many to close their doors to some or all pupils.
The DfE has said parents will "struggle to understand" why the NUT was pressing ahead with its strike.
A spokesman said: "They called for talks to avoid industrial action, we agreed to their request, and talks have been taking place weekly.
"Despite this constructive engagement with their concerns, the NUT is taking action that will disrupt parents' lives, hold back children's education and damage the reputation of the profession."
Yesterday, David Cameron's official spokesman said the Prime Minister would call on teachers not to strike because the action "disrupts children's education and children's families".
Mr Gove yesterday wrote to seven union bosses setting out the progress he believed had been made in talks between the DfE and teaching unions. In it, he said he wanted to underline his commitment to the talks process, but the NUT said the letter showed how little progress had been made in the talks.
The NUT has been embroiled in its dispute with the Government for more than two years, and staged a series of regional strikes with the NASUWT teaching union last year.
Between them they represent the vast majority of teachers.
A proposed one-day national walkout in November by the two unions was called off and the NASUWT has decided not to take part in today's strike.