Tens of thousands of schools across the UK will be closed as teachers join what is claimed by unions as the biggest public sector strike for over 30 years. The dispute over pension reforms will see the NAHT head teachers\' union striking for the first time ever. Ministers have warned that they expect more than nine out of 10 schools in England to be closed. Schools Minister Nick Gibb said it was \"irresponsible to strike while negotiations are ongoing\". Millions of pupils will see lessons cancelled as members of teachers\' unions and school support staff take part in a one-day protest over changes to their pensions. University and college students will face cancelled lectures as the UCU lecturers\' union joins the dispute. School and university staff argue that it is unfair that they are being asked to work longer and pay more for reduced pension returns. But the government says that rising life expectancy means that the current pension scheme is unaffordable - and that the revised arrangements will still represent a good deal. Pension cuts The TUC says that 30 unions are taking part in the one-day strike, the biggest such public sector walk out since the late 1970s. This will include a raft of education unions. Staff in the NUT, NASUWT and ATL are backing the strike - and for the first time in its 114-year history, the National Association of Head Teachers (NAHT) will be taking strike action. The NAHT is particularly strong in primary schools - with its membership in 85% of primary schools in England, Wales and Northern Ireland. The strike, across the UK, is supported by AHDS and EIS in Scotland, INTO in Northern Ireland and UCAC in Wales. The disputed pension changes apply to the scheme for teachers in England and Wales - but staff in Scotland and Northern Ireland are warning that the proposed shake-up could be applied to their schemes too. Unison members who provide school support services will also be joining the protest. Many parents were told last week that schools were going to be closed for Wednesday\'s strike. Local authorities have been putting lists of schools that are going to be closed on their websites. Mr Gove has indicated that he expects few schools to be open. \"I must warn parents that many schools are going to close. The overwhelming majority. North of 90%,\" he said earlier this week. It is expected that a high proportion of schools in Scotland, Wales and Northern Ireland will also be closed or disrupted. UCU general secretary Sally Hunt said: \"Our members are unlikely militants and would much rather be in the classroom than on the picket line tomorrow. \"However, they are not prepared to sit back while their living standards are attacked and will fight to protect their pensions. They want proper negotiations to secure a resolution to the dispute not more government spin.\" The NUT leader, Christine Blower, rejected claims that teachers\' pensions were unaffordable. \"This is a government that is determined to press ahead with reform regardless of need,\" she said. Mr Gibb said: \"Today\'s strikes benefit no one - they will disrupt pupils\' education; hugely inconvenience parents; and damage teachers\' reputation. \"It\'s irresponsible to strike while negotiations are ongoing. Many parents will struggle to understand why schools are closed when the pension deal on the table means that teachers will still be better rewarded than the vast majority of workers in the private sector. \"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 £5bn in 2006 to £10bn in 2016 and will carry on rising rapidly as life expectancy continues to improve. \"The Teachers\' Pension Scheme will remain one of the best available - but it\'s going to be fairer for the taxpayer by keeping costs under control.\"