Parents and pupils are facing disruption this morning as south London schools and universities are hit by a teachers' strike.
Members of the National Union of Teachers (NUT) and University and College Union (USU) are striking for one day in protest at government plans to change pensions.
And the walkout is set to disrupt dozens of schools.
A Department for Education spokesman said: “Strikes benefit no one.
"Most parents are going to be scratching their heads that schools are closed, when we’re guaranteeing teachers a far better pension than the vast majority of people in the country will ever get.
"We’ve been in serious talks for months with unions to reach a final settlement.
"These discussions are now closed and this strike, ordered by the NUT’s leaders, will not get its ordinary members any further forward.
"Reforms to public sector pensions are essential - the status quo is not an option.
"The cost to the taxpayer of teacher pensions is already forecast to double from £5billion in 2006 to £10billion in 2016 and will carry on rising rapidly as life expectancy continues to rocket."
However Dave Harvey, Croydon NUT secretary, said more than 1,000 teachers were set to walk out.
"We know of at least 45 schools that will be affected but many have not updated their status, so we are expecting more will be forced to close," he said.
The government is proposing teachers increase the contributions they make to state pensions, and the retirement age is raised to 68, while the scheme would move to an average salay payment instead of an end salary figure.
Mr Harvey said: "When we first balloted in May last year this was a proposal – now the change is in April and when teachers receive their pay check it will be less than their one in March, the first time teachers have had a pay cut since the Great depression in the 1930s."
As well as walking out, teachers and lecturers are planning to march in London before holding a rally outside the Department for Education.
Christine Blower, the NUT's general secretary, said: "Teachers cannot be expected to do anything other than defend the right to a pension which they have paid into in good faith and which the government has shown no evidence that they are either unsustainable or unaffordable.
"It is the government's intransigence and total disregard of the facts that has forced teachers to continue with this action."
And Sally Hunt, leader of the UCU, said union members had gone on strike reluctantly.
"However, it is not fair for ordinary people to suffer huge cuts in their standards of living at a time when the government is handing out huge tax giveaways to big business and high earners," she said.
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