Thousands of teachers are staging a one-day walkout in the first of a new wave of strikes over pay, pensions and conditions.
Members of the National Union of Teachers (NUT) and the NASUWT are taking part in industrial action across the north west of England. About 2,765 schools in 22 authorities will be affected, the unions claim, and rallies are due to be held in Liverpool, Manchester, Preston and Chester.
The action has been condemned by the Department for Education (DfE), which says it will disrupt pupils' education.
NUT general secretary Christine Blower said that the union "seriously regrets" the disruption the strike will cause parents and pupils. But she added: "With the profession now under serious attack from the Government, we have to take a stand to protect education and teachers. The North West will be taking the lead in sending a message to Education Secretary Michael Gove that teachers are not prepared to accept government attacks on our pay, pensions and conditions.
"Not content with wanting teachers to get less pay and retire later, Michael Gove now wants to go ahead with 'liberalising' teachers' working conditions such as the length of working days and hours and our entitlements on non-contact time and cover. Teachers are angry about the impact these imposed changes are having on the morale of the teaching profession, the recruitment and retention of teachers and on the provision of quality education for pupils."
Ms Blower insisted that the two unions were asking the Government to enter "meaningful talks" about the dispute, and that responsibility for the strike lay with Mr Gove for failing to engage with them.
NASUWT general secretary Chris Keates said that teachers were "standing up for standards". "Over the last three years, the Coalition Government has mounted savage attacks on teachers' pay, pension and conditions of service," she said. "To justify these attacks and education reforms, the Secretary of State has sought to denigrate teachers and present our public education system as broken. As a result the teaching profession is now in crisis.
"No teacher embarks on strike action lightly. No teacher has any wish to inconvenience pupils or parents or disrupt the provision of education - but a strong stand now must be made to protect the pay and conditions of service which make our schools world class."
A poll of 14,000 teachers, published by the NASUWT on Wednesday, found that teachers are increasingly unhappy with their jobs - and many are considering leaving the profession. It suggests that Government reforms to pay and pensions, as well as a heavy workload and school inspections, are to blame for dissatisfaction among the workforce.
A DfE spokeswoman said: "We are very disappointed that the NUT and NASUWT have decided to take strike action, which less than a quarter of teachers actually voted for. Industrial action will disrupt pupils' education, hugely inconvenience parents and damage the profession's reputation in the eyes of the public at a time when our reforms are driving up standards across the country."