Oliver Stephens, known as Olly, was pronounced dead at Bugs Bottom fields, Emmer Green, on Sunday.
The five teenagers, all aged 13 or 14, remain in custody, according to Thames Valley Police.
Det Supt Kevin Brown said: “Our thoughts remain with Olly’s family at this incredibly difficult time.”
He added: “This is a tragic and shocking incident which has resulted in the death of a young boy.”
The victim’s family are being supported by specially trained officers.
Highdown School and Sixth Form Centre said it was “reeling from the tragic news”.
In a statement, headteacher Rachel Cave said: “This student was part of our community and many students and staff knew him well.
“For a life to be ended at such a young age is a total tragedy. Our thoughts and prayers are with his family.”
The school, in Emmer Green, said it was arranging counseling support for students and setting up an electronic book of condolence.
Officers were called just before 16:00 GMT on Sunday following reports of an attack.
Officers are appealing for anyone who was in the area between 15:00 and 16:30 who might have taken photos or camera footage to contact them if they notice anything suspicious.
Det Supt Brown said he believed there would have been witnesses to the “dreadful incident” as the area is popular with dog walkers.
A man said his wife was walking their dog through the park on Sunday afternoon when she saw a boy on the ground with several people around him trying to give him first aid.
Another dog walker said she saw a group of young people standing in the woods in Bugs Bottom fields at about 15:30 and described it as “slightly unusual”.
Reading East MP Matt Rodda has offered his “deepest condolences” to the boy’s family.
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