TENS of thousands more teachers have joined the UK's largest education union to take part in strikes this Wednesday, according to a union boss.
Kevin Courtney, joint general secretary of the National Education Union (NEU), said ministers should be concerned about the 40,000 new sign-ups to the union since the strikes were announced.
It comes after news that schoolkids could face "super-sized" classrooms with sixty pupils from tomorrow as teachers go on strike.
Class sizes could double as at least 120,000 staff walk out across England and Wales on Wednesday.
The strike action comes after negotiation talks between Education Secretary Gillian Keegan and union bosses failed yesterday.
More than 23,000 schools will be affected in the biggest day of industrial action for a decade - with many shutting altogether.
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It means up to 4.5million schoolkids could be affected, sparking chaos for parents and pupils.
Some parents will be forced to work from home and take leave to look after younger children on Wednesday.
Downing Street has conceded that Wednesday’s mass strike action will be “very difficult” for the public.
But Mr Courtney said parents have been largely supportive of the strikes - with some expected to join demonstrations on Wednesday - as they can see "schools have been run down" and have teacher shortages.
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He said: "It's a strike against disruption in education. We want the strike to be effective because we want to concentrate the Government's mind on solving the issue."
Members of the NEU in England and Wales have demanded huge inflation busting pay rises.
But ministers say this is unaffordable and would only make inflation even worse.
Figures suggest that up to 150,000 teachers could be out on strike tomorrow and on subsequent national school strike days
Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said: "School leaders will not necessarily know who is going to be available for work until the day itself."
He said heads "are prioritising in their planning students who are taking vocational exams scheduled that day and mock exams in preparation for GCSEs and A-levels, as well as vulnerable students, while for other students there is likely to be a mixture of on-site provision and learning from home".
Walkout Wednesday will also see 500,000 other workers stay at home in scenes likened to a general strike.
Train drivers, civil servants, university lecturers, bus drivers and even security guards will all hang up their uniforms in rows over pay.