The arrest is in connection with an incident which took place at 9pm on Sunday 13 December.
The victim, a 17-year-old boy, was walking with friends in Friar Street, when they were approached by two males while outside the CEX shop.
The victim was separated from his friends by one of the males, who walked him to Victoria Park. Once there, he seriously assaulted him by headbutting, punching, kicking and stamping on his face and stomach.
The victim sustained serious eye, facial and arm injuries, which required treatment at the Royal Berkshire Hospital. He has since been discharged.
A small quantity of cash and a bus ticket were stolen during the incident.
No further action was taken against a 15-year-old boy from Wokingham who was arrested on 14 December on suspicion of robbery.
Following a public appeal for information, officers arrested a 15-year-old boy from Reading on Tuesday (5/1) on suspicion of robbery. He was released on police bail until 2 February.
The investigation is continuing and anyone who witnessed the incident who has not already spoken to police should call the non-emergency number 101 or make a report online quoting the reference 43200422617.