David Sandham collapsed at Broadoak high in Partington at 12.30pm on Tuesday and died in Trafford general hospital 35 minutes later, despite the efforts of school staff to revive him.
Police said he had been involved in an argument just before his death, although it is not yet known how he died.
A post-mortem examination has proved inconclusive but no weapons were involved, they said.
Graham Downs, headteacher, called the 400 pupils at the comprehensive for 11 to 16-year-olds to a special afternoon assembly to break the news.
The next day, students and their parents laid floral tributes at the school gates while two police officers stood guard outside.
David lived just around the corner from the school with his parents, an elder sister, aged 17, and four brothers, aged 16, 13, eight and two.
Two boys, both aged 14, were arrested on suspicion of murder and questioned by detectives. They were in custody as The TES went to press.
The death follows an attack on an 11-year-old boy in Abingdon, Oxfordshire, who was stabbed in the leg on a school bus. Two boys, both aged 11, have been bailed by police until December 15.
In July, 16-year-old Alan Pennell was sentenced to life imprisonment for stabbing 14-year-old Luke Walmsley to death in a corridor at Birkbeck secondary school in Lincolnshire.