As the Government came under increasing pressure to grant a blanket pardon to the men - many of whom are now believed to have been suffering from post-traumatic stress disorder - details came to light of how the boys met their death.
Records suppressed for 75 years show that three of the 307 were just 17 when they were shot for desertion. The records of a further 85 men do not show their ages, adding to the uncertainty over the fairness of their courts martial.
As reported in yesterday's Independent, John Reid, Minister for the Armed Forces, is reviewing the case for a pardon following the success of a campaign by Andrew Mackinlay, Labour MP for Thurrock, who believes most of those put to death were little more than confused, frightened young men.
Research by another campaigner, war veteran John Hipkin, 72, shows that the three boy soldiers who were shot at 17 - in contravention of the 1879 British Army Act - were Herbert Burden of the Northumberland Fusiliers, Joseph Byers of the Royal Scots Fusiliers, and Herbert Morris, who had travelled from Jamaica with the British West Indies Regiment.
Two others - William Hunter of the Loyal N Lancashire Regiment, and James Crozier of the Royal Irish Rifles - were shot at 18 but it is believed their offences were committed when they were 17. In any case, no one under the age of 19 should have been serving overseas at the time. Burden was just 17 years and 3 months when he was executed for desertion. At his court martial, there was no-one to speak for him because his battalion had been so decimated that all his friends and colleagues were dead, in hospital or transferred to other units.
Byers, the first under-age soldier to be shot in the war, enlisted on 20 November 1914, was shipped to France on 5 December 1914 after two weeks' basic training and was executed for desertion on 6 February 1915.
Hunter had run away at 17 after falling in love with a French girl. At his court martial, Lt Gen Henry Wilson recommended mercy but he was overruled. Wilson later became an MP and was executed by the IRA.
Crozier was recruited at 16 by an officer, Lt Col Frank Crozier, who was amused at finding a would-be recruit sharing his name. He promised Crozier's mother that he would look after her son. However, Lt Crozier later signed the boy's death warrant for desertion.
"These were just boys and the Army knew it, but they just wanted to make an example of deserters," said Mr Hipkin, whose own father lied about his age in order to fight. "God only knows how they could look into the face of a boy and sentence him to death."
The historian Julian Putkow-ski, co-author of Shot at Dawn, said: "I believe there were probably many more boys who were executed. Many lied about their ages and even their names, but none of them should have been there before the age of 19. What is more disturbing is that in some of these cases, the records show that the officers knew the men they were sentencing to death were too young and should simply have been sent home."