A pay strike by teachers on Thursday could close hundreds of schools in England and Wales.
The teachers' pay strike in England and Wales this week could damage pupils' exam revision, says the head of the school employers' organisation.
National Union of Teachers (NUT) members are staging a 24-hour walkout - the first national strike for 21 years.
Thousands of teenagers are preparing for A-levels and GCSEs - and primary pupils will soon be taking Sats tests.
Schools Minister Jim Knight says teachers "should be teaching and talking - and not walking out".
Ivan Ould, chair of the National Employers' Organisation for SchoolTeachers, says pupils will "lose out on invaluable study time".
The National Union of Teachers wants a pay rise above the proposed 2.45%.
The teachers' union is to stage a 24-hour walkout on Thursday - the first national strike for 21 years.
The NUT says the action could be called off if there is a rise linked to the Retail Prices Index inflation measure, which stood at 3.8% in March.
The NUT says the action could be called off if there is a rise linked to the Retail Prices Index inflation measure, which stood at 3.8% in March.
The government, which is giving a 2.45% rise this year, says a strike will only disrupt children's learning.
The union's acting general secretary, Christine Blower, has warned that "three years of below-inflation awards for teachers continues to have a damaging effect on teacher recruitment and retention".
But employers' leader Mr Ould criticised the timing of the strike: "Children so close to their exams will lose out on invaluable study time and parents will lose out as they are forced to take unnecessary holiday to look after them."
Uncertain impact
Uncertain impact
"I am disappointed by the decision to strike, as I think parents will be - and as will the majority of teachers who did not vote to strike," said Mr Knight.
In an attempt to reduce the impact on pupils who are revising, some schools will be arranging to keep classes open specifically for those about to take GCSEs and A-levels.
Teachers should be teaching and talking - and not walking out Jim Knight, Schools Minister
The government has criticised the decision to take strike action.
"We believe that all teachers should be teaching and talking - and notwalking out next week," said Schools Minister, Jim Knight.
It remains uncertain how many schools or individual classes will be affected by the union's one-day protest.
It remains uncertain how many schools or individual classes will be affected by the union's one-day protest.
A projection based on a survey of 25 local authorities by the Guardian suggests that more than 1,000 schools could be closed by the strike.
A projection based on a survey of 25 local authorities by the Guardian suggests that more than 1,000 schools could be closed by the strike.
An earlier online poll by the Times Educational Supplement suggested that half of schools could be disrupted.
An earlier online poll by the Times Educational Supplement suggested that half of schools could be disrupted.
There are more than 17,000 primary schools in England and 3,300 secondary schools.
There are more than 17,000 primary schools in England and 3,300 secondary schools.
Ministers have announced that this year's 2.45% rise for teachers will be followed by 2.3% rises in 2009 and 2010.
Ministers have announced that this year's 2.45% rise for teachers will be followed by 2.3% rises in 2009 and 2010.
In an NUT ballot of members, voting was 48,217 (75%) in favour of strike action and 15,884 (25%) against on a 32% turnout.
In an NUT ballot of members, voting was 48,217 (75%) in favour of strike action and 15,884 (25%) against on a 32% turnout.
Teachers should be teaching and talking - and not walking out Jim Knight, Schools Minister
Some schools have sent written confirmation that they will shut on Thursday, but many teachers, pupils and parents will not know until this week whether their schools will be closed by the strike.
Some schools have sent written confirmation that they will shut on Thursday, but many teachers, pupils and parents will not know until this week whether their schools will be closed by the strike.
Parents are advised to check directly with their children's school if they are unsure whether they will be affected by the dispute.
Parents are advised to check directly with their children's school if they are unsure whether they will be affected by the dispute.
Strike rallies are being organised in towns and cities around England and Wales.
Strike rallies are being organised in towns and cities around England and Wales.
Legal action
Legal action
The strike is being organised by only one teachers' union - which will mean that in some schools some individual classes will be closed for the day while others, where teachers belong to other unions, will remain open.
The strike is being organised by only one teachers' union - which will mean that in some schools some individual classes will be closed for the day while others, where teachers belong to other unions, will remain open.
Special needs school Harford Manor, in Norwich, is staying open but closing three classes on Thursday because half its staff of 10 are NUT members and supporting the strike.
Special needs school Harford Manor, in Norwich, is staying open but closing three classes on Thursday because half its staff of 10 are NUT members and supporting the strike.
Head teacher Geoff Kitchen said 21 of the 76 pupils would be affected by the selective closures.
Head teacher Geoff Kitchen said 21 of the 76 pupils would be affected by the selective closures.
He added: "We went to parents last week and said 'we are closing five classes' but we have since reduced that to three.
He added: "We went to parents last week and said 'we are closing five classes' but we have since reduced that to three.
"It's a reasonably difficult decision to make to close these classes.
"It's a reasonably difficult decision to make to close these classes.
"On the letter I sent out to parents I put at the bottom that if they wished to discuss it further they could, but only one parent called me."
"On the letter I sent out to parents I put at the bottom that if they wished to discuss it further they could, but only one parent called me."
'Refused'
Elsewhere, although most GCSE exams do not begin for some weeks, one parent is worried that her daughter's art exam could be interrupted by the strike.
Julie Williams said: "Does the union not have an exam timetable? Are they incompetent? To ask teachers to walk out during a GCSE exam seems ludicrous.
"My daughter's school has two art teachers with examination classes who have been asked to strike during the exam.
"One has quite rightly refused to do so. The other is striking and I presume all the children will now be disadvantaged as one conscientious teacher tries to help both groups complete their exam."
The Local Government Association said parents could sue their local authority if their school failed to provide an extra day's teaching to make up for lost teaching time.
The Department for Children, Schools and Families said it had nothing to add at this stage.
About 27,500 Lecturers from the University and College Union are taking strike action on the same day over pay.
Are you a teacher that will be taking part in the strike action on Thursday? Could your school face closure on the day? Send us your comments by filling out the form below.
Are you a teacher that will be taking part in the strike action on Thursday? Could your school face closure on the day? Send us your comments by filling out the form below.
