Britain's biggest teachers' union has accused the Ministry of Defence of breaking the law over a lesson plan drawn up to teach pupils about the Iraq war. The National Union of Teachers claims it breaches the 1996 Education Act, which aims to ensure all political issues are treated in a balanced way.

Teachers will threaten to boycott military involvement in schools at the union's annual conference next weekend, claiming the lesson plan is a "propaganda" exercise and makes no mention of any civilian casualties as a result of the war.

They believe the instructions, designed for use during classroom discussions in general studies or personal, social and health education (PSE) lessons, are arguably an attempt to rewrite the history of the Iraq invasion just as the world prepares to mark its fifth anniversary.

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Steve Sinnott, the general secretary of the NUT, said: "This isn't an attack on the military – nothing of the sort. I know they've done valuable work in establishing peace in some countries. It is an attack on practices that we cannot condone in schools. It is a question of whether you present fair and balanced views or put forward prejudice and propaganda to youngsters."

At the heart of the union's concern is a lesson plan commissioned by an organisation called Kids Connections for the Ministry of Defence aimed at stimulating classroom debate about the Iraq war.

In a "Students' Worksheet" which accompanies the lesson plan, it stresses the "reconstruction" of Iraq, noting that 5,000 schools and 20 hospitals have been rebuilt. But there is no mention of civilian casualties.

In the "Teacher Notes" section, it talks about how the "invasion was necessary to allow the opportunity to remove Saddam Hussein" but it fails to mention the lack of United Nations backing for the war. The notes also use the American spelling of "program".

Addressing whether the MoD should be providing materials for schools, Mr Sinnott said that he did not object, as long as the material was accurate, presented responsibly and contained a balanced view of opinions.

The union has protested to the Schools Secretary, Ed Balls, who has referred the complaint to the MoD. In a letter to Mr Balls, Mr Sinnott said: "I have to say that were the MoD pack to be distributed and followed without the legally required 'balanced presentation of opposing views' there would, in my view, be very serious risk of a finding of non-compliance with section 406 (of the 1996 Education Act) at least.

"I do not doubt that there would be many members of this union who would not accept as 'fact' the assertions made particularly in the Teacher Notes, nor, I think, could some of the assertions made in the Student Worksheet be regarded as non-controversial."

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Mr Sinnott reminded Mr Balls that a High Court judge had ruled that the film An Inconvenient Truth, by the Oscar-winning former American vice-president Al Gore, could not be used in schools without teachers counteracting some of the assertions made in it.

Mr Balls sought to distance himself from supporting the material.

He said: "I am sure you are aware my department does not promote or endorse specific resources or methods of teaching for use in schools but I appreciate you drawing this to my attention." Mr Balls added that he had instructed his officials "to take this matter up" with the MoD.

A spokesman for the MoD said the ministry had consulted with interested parties over the proposed lesson plan in order to ensure it had the support of the education community. "We did ask the Stop The War coalition to take part although it refused."

The spokesman added that the programme was "a set of web-based resources" whose use was "completely voluntary".

"We have consulted widely with teachers and students during the development of these products and feedback from schools has been extremely encouraging," he added.

"Teachers and students found them to be valuable and fun resources for applied learning.

"They are designed to support teachers in delivering a whole range of subjects across the national curriculum and its equivalents in Scotland and Wales.

"We are happy to engage with the NUT and we will be writing to them."

Union members say they are also worried that armed forces recruitment fairs in schools glamorise the job by citing exotic countries that recruits will visit but fail to mention that they may be required to kill people.

According to an independent assessment of the MoD's recruitment material by the Joseph Rowntree Trust, however, the material concerned was "very dubious". The trust said it had used misleading marketing with advertising campaigns that "glamorise warfare, omit vital information and fail to point out the risks and responsibilities associated with a forces career".

Mr Sinnott said: "On their recruitment material, it tells what an exotic lifestyle this can be, but it doesn't mention that being in the military involves killing people. These things don't feature as they should in a proper, balanced view of what it is like being in the armed forces."

What the MoD's guide says... and what it omits

* "Iraq was invaded early 2003 by a United States coalition. Twenty-nine other countries, including the UK, also provided troops... Iraq had not abandoned its nuclear and chemical weapons development program". After the first Gulf War, "Iraq did not honour the cease-fire agreement by surrendering weapons of mass destruction..."

The reality: The WMD allegation, central to the case for war, proved to be bogus. David Kay, appointed by the Bush administration to search for such weapons after the invasion, found no evidence of a serious programme or stockpiling of WMDs. The "coalition of the willing" was the rather grand title of a rag-tag group of countries which included Eritrea, El Salvador and Macedonia.

* "The invasion was also necessary to allow the opportunity to remove Saddam, an oppressive dictator, from power, and bring democracy to Iraq".

The reality: Regime change was not the reason given in the run-up to the invasion – the US and UK governments had been advised it would be against international law. Saddam was regarded as an ally of the West while he was carrying out some of the worst of his atrocities. As for democracy, elections were held in Iraq during the occupation and have led to a sectarian Shia government. Attempts by the US to persuade the government to be more inclusive towards minorities have failed.

* "Over 7,000 British troops remain in Iraq... to contribute to reconstruction, training Iraqi security forces... They continue to fight against a strong militant Iraqi insurgency."

The reality: The number of British troops in Iraq is now under 5,000. They withdrew from their last base inside Basra city in September and are now confined to the airport where they do not take part in direct combat operations.

* "The cost of UK military operations in Iraq for 2005/06 was £958m."

The reality: The cost of military operations in Iraq has risen by 72 per cent in the past 12 months and the estimated cost for this year is £1.648bn. The House of Commons defence committee said it was "surprised" by the amount of money needed considering the slowing down of the tempo of operations.

* "Over 312,000 Iraqi security forces have been trained and equipped (Police, Army and Navy)."

The reality: The Iraqi security forces have been accused, among others by the American military, of running death squads targeting Sunnis. In Basra, the police became heavily infiltrated by Shia militias and British troops had to carry out several operations against them. On one occasion British troops had to smash their way into a police station to rescue two UK special forces soldiers who had been seized by the police.

* "A total of 132 UK military personnel have been killed in Iraq."

The reality: The figure is 175 since the invasion of 2003. A British airman died in a rocket attack at the airport two weeks ago despite British troops not going into Basra city on operations. Conservative estimates of the number of Iraqi civilians killed since the beginning of the invasion stand at around 85,000.

* "From hospitals to schools to wastewater treatment plants, the presence of coalition troops is aiding the reconstruction of post-Saddam Iraq."

The reality: Five years after "liberation", Baghdad still only has a few hours of intermittent power a day. Children are kidnapped from schools for ransom and families of patients undergoing surgery at hospitals are advised to buy and bring in blood from sellers who congregate outside.

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