A teenager made a "throwaway" comment about suicide hours before he was found hanged, an inquest has been told.
Sam Leeson, 13, from Gloucester, was found dead in his bedroom last June.
The inquest into his death heard he had replied "you could kill yourself" when asked at school for possible solutions to the population explosion in China.
Giving a narrative verdict, the coroner said he was not sure if Sam's actions were deliberate or the unintended consequences of "experimental action".
No evidence of "cyber-bullying" was found by police computer experts, the inquest was told, nor did his family or school provide evidence of any "traditional" bullying to the hearing.
Coroner Alan Crickmore was told Sam's comment about suicide to a teaching assistant was not mentioned by the assistant at the Severn Vale School in Quedgeley, although head teacher Peter Rowland said all such comments would now be logged as a matter of policy.
Speaking after the inquest, Sam's mother, Sally Cope, a 47-year-old skills tutor, claimed her son, who often wore black clothes and was a fan of the "emo" rock genre, was told to "cheer up" after making the comment in class.
"Raising the alarm about his possible state of mind might have saved him," she said.
In a statement she said: "This out-of-character statement should have been flagged and reported to senior staff members and to us."
"One telephone call may have saved his life and I know if he had been disruptive in class, had forgotten homework or had the wrong sports socks, I would have been contacted."
Head teacher Mr Rowland said: "Sam's death was a tragedy. He was a very special young person. He will never be forgotten and he does indeed leave a powerful legacy.
"We hope that can be of some consolation to a grieving family at this most difficult of times."