One in four schools across Wales will be affected by the teachers’ planned walk-out on Thursday.

Members of the National Union of Teachers (NUT) are staging the action in a long-running row over pay.

A BBC Wales survey has found that at least 500 schools will close or cancel at least some lessons in the first strike by the NUT in 21 years.

The Westminster government has offered a pay deal worth 2.45% but union leaders want 4.1%.

The snapshot of action across in Wales has shown that Caerphilly will be one of the worst-hit counties - 69 schools there will be affected by the action.

It is thought around 303 schools will close outright and 212 will partially shut on Thursday, according to BBC Wales research.

Rallies planned

NUT Wales secretary David Evans said a below inflation pay cap on public sector pay is “patently unfair.”.

He added: “No matter how just your case is for higher pay, the shadow of Gordon Brown looms large over negotiating table.

“In these circumstances, we feel it is important that public sector workers unite around a common cause - the right to decent, inflation matching pay awards.

“On Thursday there will be rallies in Cardiff and Wrexham in protest against the way that teachers and other public sector workers are being treated,” he added.

The NUT has not ruled out further strikes.

The union has 16,500 members in Wales.