When the independent-school student investigated the war-time roles of Jozef Ostrowski and Guglielmo Fusi, the 14-year-old found that history came alive and his research revealed the complexity of conflict better than any textbook.
William, a Manchester Grammar pupil, said: "They were conscripted to fight in a war they never really understood, watching their friends die and suffering terrible atrocities in prisoner-of-war camps."
The teenager discovered his Polish grandfather Jozef fled to the Soviet Union when the Germans invaded in 1941. There he joined the Polish Army and fought for the Allies.
His paternal grandfather, Guglielmo, had completed his national service in Italy and was flying planes in the Far East when he was called up.
After interviewing relatives and poring over old documents and records, William uncovered the hardships endured by the two men.
John Shoard, history teacher at Manchester Grammar, said that he had invited the boys in the class to do some history research in their own time.
"William's project was research into the Second World War with a family history dimension. He is a very clever boy and has done something special - it is a fantastic story."
From Jozef's recollections to others, William wrote about his grandfather's experience at the fourth battle of Monte Cassino when he spared the life of an enemy soldier.
"I was leading the taking of another German defence. Four Germans came out of the station firing at us. They killed two of my colleagues. We killed three. The other was praying to God. He said: 'I have a wife and three children at home, please let me see them again.' He was just fighting because he had to. He didn't want to be there any more than I did."
Guglielmo recalled coming across a British pilot. "His parachute had not opened as he baled out. His was one of the faces I always remembered. Maybe it was the bewildered expression or the realisation that he was a young man like myself, who missed his mother's cooking. I covered him with his parachute and weighted it down with stones."
The school's High Master, Dr Martin Stephen, said the project was practically ready for publication. "What this young man has managed to produce is a genuinely moving piece of history. This is not a schoolboy project, it is real history," he said.