A 15-year-old boy who was fatally stabbed at a school in Sheffield has been described as a "lovely lad" and the "life of a party".
Floral tributes and messages have been left outside All Saints Catholic High School, where the boy, named locally as Harvey Willgoose, was injured.
A boy, 15, has been arrested on suspicion of murder and remains in police custody, South Yorkshire Police said.
The force said it was working "at pace" to build a full picture of what had happened.
One message left outside All Saints described the teenager as someone who had been "the life of a party" and who had "brought joy and laughter to everyone who knew him".
His "bubbly personality was contagious", it added.
"I'll never forget all the moments, all the laughs. You'll be missed by so many," it said.
A teenager who said he had known the 15-year-old also left a bunch of flowers outside the school.
The 17-year-old, who studies at a local college, heard the news through friends and said the boy who died had been a fan of Sheffield United.
He said: "I'm a bit upset to be honest, it came as such a shock.
"He seemed quite a happy guy and a nice guy to be around."
One All Saints pupil said the victim had been a "lovely lad".
"He would make your day better hearing him down that hallway. You didn't have to personally know him to be upset," the 17-year-old said.
"Teachers loved him, students loved him, everyone loved him.
"I've been at the school for seven years now and nothing like this has ever, ever happened."
Asked about the incident while on a trip to Brussels, Prime Minister Sir Keir Starmer said his first thoughts "as a father" were with the victim's family.
"The terrible stabbing in Sheffield is one where I think the whole country would want to reach out to the family, to the friends, to the school, the entire community in their grief and mourn with them," he said.
Louise Haigh, the MP for Sheffield Heeley, said the news was "horrific" and that "serious questions" would have to be answered about how it could have happened.
Anti-knife crime campaigners in the area have said incidents like this should not happen.
Amaan Ahmed, who manages the Castle Asian Community Trust near the school, said he feared the boy's death would leave parents wondering if they should send their children back to school.
"If it can happen in a public place like a school, people will be worried about going to the park I think too," he added.
Sheffield-based Anthony Olaseinde, who works for the charity Always an Alternative, said the incident was "heart-breaking".
"Something like this should not happen," he said.
He said the charity had held sessions at All Saints and worked with young people at the school.