School children across the UK have been marking the anniversary of 11 September in special assemblies.

Some schools are expected to observe the two minute silence at 13.46, but many will not, as head teachers say they did not get enough notice.

At Sandringham School in St Albans, Hertfordshire, children will observe the silence.

Head teacher Janet Lewis says pupils were badly affected by the events at Ground Zero.

I was frightened, I thought it was Armageddon

Adam, pupil

"At that time we marked what had happened with a two minute silence and a special 'Thought for the day' at assembly," she said.

"We encouraged children to talk about it all and that is what we are continuing to do.

"There is a lot of talk about children being de-sensitised to violence because of the films they watch but I don't think that is true."

One pupil who was deeply upset by what happened was teenager, Adam,.

"I was really shocked and felt so physically sick I was off school for two days," he said.

"I was frightened, I thought it was Armageddon.

"Now, with all this Iraq business, it's terrible. There's still a lot of bad things happening."

Head teacher Janet Lewis: "We encourage them to talk about it"

John Dunford, the general secretary of the Secondary Heads Association (SHA), said schools were observing the date and would no doubt be encouraging children to think about the significance of it.

"I think schools will, as indeed they do with Remembrance Day, go beyond the simple act of remembrance to try and bring young people to a better understanding of the issues of what happened, " he said.

He added: "The observance of two minutes' silence at 13.46 may not have been widely publicised enough in time for all schools to make the necessary arrangements.

"But I am sure that many schools will want to mark the occasion respectfully."

Unpatriotic

In the United States, the biggest teachers' union, the National Education Association, has been criticised by some people over lessons plans it published on its website on how to tackle 11 September.

Critics said the plans were not patriotic enough, saying attempts to ask why the attacks happened justified the terrorism.

SHA general secretary John Dunford said head teachers were used to handling such sensitive subjects.

"That is just the kind of sensitive situation that head teachers frequently face when doing school assemblies.

"I think they are accustomed to walking the tightrope."