Thames Valley Police said the five teenagers, aged between 13 and 14 and from Berkshire, are being held on suspicion of conspiracy to commit murder.
It comes after officers were called to reports of a stabbing in Bugs Bottom fields, Emmer Green, just before 4pm on Sunday.
The victim, named by police as Oliver Lucas Stephens, known as Olly, was pronounced dead at the scene.
Thames Valley Police said in a statement on Monday: “He [the victim] has now been identified as Oliver Lucas Stephens, known as Olly, from Reading.
“His family are being supported by specially trained officers and we would ask that their privacy is respected at this extremely difficult time.”
The five youngsters arrested following the incident remain in police custody, the force said.
Senior Investigating Officer Detective Superintendent Kevin Brown, head of Thames Valley Police's Major Crime Unit, added: "Our thoughts remain with Olly's family at this incredibly difficult time.
"I would urge anyone who has any information that they believe is relevant to this investigation, no matter how small you think it is, to please get in touch."
Several officers on Monday morning stood guard at police cordons erected at Bugs Bottom Fields, one blocking a road around it and another sealing off access to an open patch of grass.
Some early-morning dog walkers had to turn back after seeing the police tape.
The area is less than a mile from Highdown School and Sixth Form Centre.
Matt Rodda, Labour MP for Reading East, told the PA news agency near the scene: "I offer my deepest condolences to this poor lad's family and friends.
"I was deeply shocked by it, apparently this poor lad was barely 13 years old.
"It's quite astounding really. It must have been truly dreadful to be here at the time.
"This is a very quiet area, a suburban area on the edge of town and typically on a Sunday afternoon, when the incident happened, you would have a lot of families, people walking their dogs in this country park, [a] well known beauty spot which is very quiet and pleasant."
Police Federation chairman John Apter tweeted: “Horrific, so many lives will be shattered by this. Society does indeed need to take a look at itself.”
Anyone with information is asked to call police on 101 or Crimestoppers anonymously on 0800 555111.
Additional reporting by PA