Widespread disruption is likely in a number of both inner city and rural areas. Leeds, Cardiff, Suffolk and Cumbria all look likely to have many schools shut or partially closed.
And as head teachers get a clearer picture of staffing for the strike day, the proportion of schools set be disrupted is climbing upwards - approaching one in three schools.
The strike day is likely to cause childcare problems for parents - and an agency specialising in short-notice childcarers has reported a five-fold increase in inquiries.
"Many parents have only just finished the Easter holidays so it is hard for them to take more time off work," says a spokesman for Emergencychildcare.co.uk.
Anglesey - 51% closed
Blackpool - 55% closed or partially closed
Denbeighshire - 43% closed
Newcastle - 69% closed or partially closed
North Tyneside - 64% closed or partially closed
Nottingham - 37% closed
Some parents with more than one child face having one at home and the other in school - even within the same school, where only some classes are affected.
They are likely to get letters warning them not to keep both children at home. If one of the children is not affected by the strike, their absence will be treated as unauthorised.
One headteacher on why she will be closing her school
The strike sees the teachers' union pitched against the government's constraints on public sector pay - with the NUT and the government arguing over which measure of inflation should be used to determine pay increases.
"What we're saying to the government is, if you really do value teachers, then make sure that they're paid at least at the level of inflation - which we take to be the RPI, which is 4.1%," says the union's acting head, Christine Blower.
The pay deal which the union is attacking represents a 2.45% rise this year with a further rise of 2.3% in 2009 and 2010.
The government says it has increased teachers' pay by an average of 19% in real terms since 1997.
Prime Minister Gordon Brown told MPs: "I think it is very regrettable that the teachers are going on strike tomorrow, and the reason is that even the chairman of the Pay Review Body has said this is an independent award, independently adjudicated, and one that the teachers should be prepared to accept and I hope that, after reflection, the teachers will reconsider that they're going to take in future on this matter."
Shadow schools minister Nick Gibb agreed.
"Many children have important exams coming up soon and can't afford to miss crucial lessons, and many parents will have to miss work to look after them," he said.
Liberal Democrat schools spokesman David Laws aid he did not support the action and called for a no-strike agreement between teachers and employers.
"Given the importance of education, we should be trying to move to a presumption that teaching unions will not take strike action," he said.
"The government should open talks with all unions to see how the independent pay review process could be strengthened to help both sides to agree such an approach."
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