American teaching unions argue over what children should be told about 11 September

Tens of millions of American children return to school today – and straight into a classroom feud about 11 September and the lessons they should be taught about the terrorist attacks whose first anniversary is fast approaching.

The dispute has simmered pretty much since the day itself, becoming part of the country's endless culture wars between liberals and conservatives. For the former, 11 September underlines the need for tolerance, forgiveness and the acceptance of diversity.

For conservatives, the anniversary is all about "moral clarity," and recognition that the attacks were evil deeds perpetrated by unequivocally evil terrorists.

Nowhere though is the argument sharper than between the country's two largest teachers' unions, the 2.7 million strong National Education Association (NEA) and its smaller rival, the American Federation of Teachers, which believes that in its concern not to apportion blame for the attacks the association has caved in to the political correctness lobby.

Children should have a factual understanding of 11 September, says the federation, arguing that lessons should be based on "what is undisputed about the terrorists who are to blame for the attack on America and whose values are anathema to ours". Anything that seemed to blame the US for the attacks was wrong, the federation continued, as it poured scorn on "well-meaning lesson plans" that avoided explicit judgement about the aims and character of the terrorists.

Twisting the knife further, the federation added that, of course, "not for one moment do we believe that the NEA is unpatriotic", and efforts to portray it as such were "just dead wrong."

The NEA hit back by accusing its critics of plumbing new depths by taking the various proposed 11 September curriculums out of context, to exploit America's greatest modern tragedy for cheap political points.

But the NEA was stung enough by charges that it was promoting "psychobabble" to pull the material from its website.

One proposal generating controversy was that students read and discuss a fictional story entitled, "My Name is Osama, about an immigrant Iraqi boy whose family moves to the US, and then finds himself bullied by his American classmates because of his name and heritage. The trouble is only defused when the headmaster talks of his own family history to help Osama put the episode in perspective.

That was too much for exponents of the "moral clarity" beloved of President Bush. "What we learnt on 11 September was not that Americans discriminate against Arabs," says Bill Bennett, a leading conservative and a former education secretary in Republican administrations. He adds that, despite blemishes, America has a good overall record of promoting peace and justice. "Teachers must be willing to say that there are moral absolutes." Mr Bennett insists.

At this point the dispute moves directly into the political arena, echoing President Bush's insistence that terrorism is always evil, and the world has to choose either to support the United States or be counted against it.

In a suggested curriculum co-written with Lynne Cheney, wife of the Vice-President and another conservative stalwart, Mr Bennett attacks "the dangerous idea of moral equivalence", and "the usual pap about diversity" put out by the NEA and its backers.