Media playback is unsupported on your device Media caption Christine Blower, NUT: "This is the time that we have to take action"

Thousands of schools in England and Wales were closed on Wednesday, as teachers joined picket lines in action over pay, pensions and conditions.

The strike was staged by members of the National Union of Teachers (NUT).

Union leaders said the action had been a "clear demonstration" that teachers were thoroughly tired of "intolerable pressures" from the government.

The Department for Education (DfE) claimed only 12% of schools in England were forced to close completely.

NUT general secretary Christine Blower said the one-day national walkout had been a success and did not rule out further strikes next term.

"Today has been a clear demonstration that teachers are thoroughly tired of the intolerable pressures they are being put under by the coalition government," she said.

"Teachers love teaching but are crushed by the long hours and stifling accountability regime.

WHAT WAS THE SCALE OF THE STRIKE? Today's action was taken by the NUT alone. The NASUWT, which had taken part in industrial action prior to the government agreeing to talks, decided not to walk out. The NUT has 326,930 members across England and Wales. There are some 24,330 schools in England and 1,700 in Wales. The union claimed the strike was a success, but the Department for Education said only 12% of schools in England had to close fully. For working families affected though, the strike meant having to pay for additional childcare, asking favours of family members or using up annual leave. Education Secretary Michael Gove is currently holding discussions about performance-related pay, pensions and conditions with seven teaching unions - NASUWT, ATL, ASCL, NAHT, UCAC and Voice, as well as the NUT.

"If there isn't movement in the talks there could well be further strike action this summer - perhaps [Schools Minister] David Laws can persuade [Education Secretary] Michael Gove to avoid that."

But the DfE said only about 2,920 of England's 24,330 schools were forced to close completely on Wednesday - based on calls to every school and local authority, with a response rate of 90% .

By comparison, officials said, around 60% of schools were closed during the public sector workers' one-day national strike over pension changes in November 2011.

Leaked memo

The NUT has been embroiled in its current dispute with the government over pay, conditions and pensions for more than two years, and staged a series of regional strikes, together with the NASUWT teaching union, last year.

A proposed one-day national walkout in November by the two unions was called off in the wake of talks with the government and the NASUWT has decided not to take part in this latest strike because the government had engaged in a debate.

A leaked memo from the NASUWT claimed some members have faced insults and intimidation from NUT members over their decision not to take action. But the NUT denied any negative campaigning from its headquarters.

Ms Blower told the BBC that talks with the government had not produced the right outcomes and that teaching was becoming "unmanageable" with primary school teachers working 60-hour weeks and secondary school teachers working 56 hours.

Image caption Welsh NUT members took their protest to the Welsh Assembly in Cardiff Bay

'No basis for strike'

But Mr Laws told the BBC there had been no basis for Wednesday's strike.

He said: "I do not understand why the NUT are taking this industrial action in the middle of talks."

Mr Laws said he was currently in talks with seven trade unions, but only the NUT had chosen to strike.

Media playback is unsupported on your device Media caption Sally Gould recorded her daily routine for BBC Radio 5 live

A spokesman for the DfE said: "The NUT has tried to create as much disruption for pupils and parents today as possible.

"In spite of this, thanks to many hard-working teachers and heads, only 12% of schools across the country were closed today. This is by far the lowest level of support for any national teachers' strike since 2010.

Image caption The action means thousands of children missed lessons

"They [the NUT] called for talks to avoid industrial action, we agreed to their request, and talks have been taking place weekly. Despite this - and without the support of any of the other six unions engaged in the talks - the NUT has today taken industrial action.

"While the impact in many schools has been negligible, it has disrupted parents' lives, held back children's education and damaged the reputation of the profession."

Image caption NUT members are angry at changes to pay, pensions and working conditions

As a result of the NUT's action on Wednesday, many schools were closed, while others had to cancel particular classes, depending on the proportion of NUT members on the staff.

Image caption Around 2,500 striking teachers marched in central London

While the DfE says only 12% of schools in England were closed, the BBC understands there were 472 partial closures and 297 full closures in Wales, out of a total of more than 1,700 schools.

In these areas of England, the BBC learnt at least the following numbers of schools were affected:

the North East and Cumbria - about 400

Hampshire, Berkshire, Dorset, Oxfordshire and the Isle of Wight - more than 300

Birmingham and the Black Country - almost 200

Sussex - 170

Essex - more than 100

Norfolk - 77

Suffolk - 13

Kent and Medway - 60

Cambridgeshire and Peterborough - 90

Devon and Cornwall - 80

Staffordshire - 50

Coventry - 12

Shropshire - 33

Warwickshire - 80

Hereford and Worcestershire - 30

The union said Wednesday's strike action was covered by two ballots held in May 2011 and June 2012.

The turnout for the ballot was 40% and 92% of these members voted in favour of strike action. The NUT has 326,930 members in England and Wales.