When Harry Patch was the same age as some of the students he spoke to in his final years, he had a two-inch piece of shrapnel removed from his leg without anaesthetic.
The last-surviving First World War veteran, who died this week aged 111, was 18 years old when he joined the army in 1916 and went to fight in the trenches of Flanders.
It was an experience that he spoke about extensively in schools during his last decade in an effort to ensure that today's generation never have to suffer anything similar.
Teenage Harry was sent to the trenches at Passchendaele, near Ypres, after six months' training with the Duke of Cornwall's Light Infantry. Two weeks later, he was at Pilckem Ridge.
"I could see the bewilderment and fear on the men's faces as we went over the top," the former private remembered.
"We crawled, because if you stood up you'd be killed."
He was wounded by a shell that also killed three of his comrades. Because the medical station had run out of anaesthetic, he was held down by four men, while the surgeon removed the shrapnel.
After the war, Harry did not speak about his experiences, even to his wife and two sons.
It was only after he was admitted to a home for the elderly, shortly after his 100th birthday, that his wartime memories were stirred up again. And so he began touring schools and colleges, talking about his experiences in the trenches. He wanted to remind the younger generation of the sacrifices that his own had made, and to persuade them that no war was worth any soldier's death. A committed pacifist, he often emphasised the fact that he had never killed a man.
Speaking to a group of Hertfordshire pupils in 2003, Mr Patch said: "It was lousy in the trenches - filthy and unsanitary. "You never forget the expressions on people's faces when they went over the top. I don't think today's teenagers realise what war is."