By Chris Hogg
BBC News, Tokyo
An elderly man shuffled through the door of the classroom on the top floor of the Hiroshima Kokusai Gakuin High School.
The class of young teenagers watched in silence as he slowly and deliberately pulled some pictures out of his bag and propped them against the blackboard.
Yukio Yoshioka said Japan was both an aggressor and a victim
They showed young Japanese with horrific burns.
He unfolded a map of Hiroshima. There was a big red circle drawn around the centre of the city.
Finally he turned to the class and cleared his throat.
"It was hell," he said.
Yukio Yoshioka, 76, is what is known in Japan as a "hibakusha" - the word means a survivor of the atomic bombing.
When he was the same age as these schoolchildren he suffered terrible burns in the Hiroshima attack.
Now a pensioner, he's trying to pass on to a new generation the horrors of the atomic bomb.
It is not an easy task.
A new generation
The children sat impassively. As I watched them, it was hard to tell what they were feeling.
Before the class had started, they had been as rowdy and noisy as any teenagers anywhere else in the world.
But as they listened to him they were silent. No one asked any questions. Some of them, I'm sure, had heard this before.
Afterwards I asked him why he had come to the school.
"I feel it's important to try to make sure it never happens again," he said.
"We were the offending side, but also the victims. We harmed people in China, Korea and South East Asia. But the A-bomb was dropped on us, so we understand how difficult and terrible war is.
"We can understand how other people feel. We can see their point of view. I think that's what all the A-bomb survivors feel."
Further down the hall, another hibakusha was close to tears as she related her story to a class of children.
Despite the summer heat, Junko Kayashige was wearing a rather formal dress with a high neck.
"I try to cover my neck because of the damage," she said.
Ms Kayashige was six years old when the bomb was dropped on her city.
The scars she bears have been an embarrassment to her throughout her life.
Like many hibakusha she has suffered a great deal of discrimination from other Japanese, and that is why so many keep quiet.
But Junko Kayashige is different. She took the class back to that bright morning on 6 August 1945.
She said she remembered seeing the plane, and then experiencing the blast.
"When I came back to my senses," she said, "I found myself lying on the dirt ground under the window inside the house. My cousin was lying there too. My aunt and sister, who had been in the same room, had been blown further into the house."
In this classroom, the pupils did ask a couple of questions at the end.
One told her his grandfather's most frightening memory was of the piles of dead bodies waiting to be burned.
"I agree with your grandfather," she said. "The images of the dead stayed with me for months. In fact, the stain left by one corpse on the street was visible for weeks. But unless you move on, put it behind you, you can't get on with your life."
"I just want to talk while I can still talk," she told me afterwards.
"It doesn't matter if the young people understand or not - I just have to keep talking to them."
Junko Kayashige wears high-necked tops to cover her scars
The two hibakusha later met with others who had gone to see different classes, and they chatted about how the morning had gone.
"The other day I saw on television that talks on the non-proliferation treaty had broken down," said Ms Kayashige.
"It made me think that is partly because of the hibakusha's negligence. We haven't said enough to let the world know about the reality of the atomic bomb, especially in the United States. The US has the information but ordinary people don't know enough about it."
Mr Yoshioka agreed. "We really should eliminate war. It is the wish of those of us who experienced it. I want to pass on that wish to young people. That's why we're here today."
The average age of the hibakusha is now 72. It is hard to tell exactly how many are left, because many of those who survived the bombing kept quiet for fear of discrimination.
As well as visiting schools, hibakusha give talks to students in the city's Peace Park and work as peace volunteers in the city's museum.
Some find modern parallels to their suffering.
"When I see the children who've been bombed in Iraq," one woman told me, "I know why I have to carry on speaking out. We'll continue speaking out until people stop using these weapons."