The juvenile has been found guilty of rape and murder and sentenced to three years in a correctional home.
The board, presided over by Principal Magistrate Geetanjali Goel, pronounced the verdict and acquitted him of some of the charges.
"The juvenile has been found guilty under rape and murder charges, and accordingly sentenced to three years of jail," Rajesh Tiwari, a lawyer for the juvenile, told reporters.
The lawyer said the juvenile would be sent to a reform home to serve the term, taking into account the months he has already spent in detention since his arrest.
The gruesome incident occurred in south Delhi when a 23-year-old female physiotherapy intern was gang-raped in a bus that she and her male companion had boarded.
The boy, who was 17-and-half years old at that time, has since turned 18.
The police had in its charge sheet stated that juvenile was the most brutal of all accused.
A native of Uttar Pradesh, the minor had moved to Delhi at the age of 11 and was arrested after the incident from Anand Vihar in east Delhi.
Five others were arrested in the case. While accused Ram Singh, Mukesh, Pawan Gupta, Vinay Sharma and Akshay Thakur were tried by a fast-track court in Saket in south Delhi, the juvenile's case was heard by the board.
The case against Ram Singh was dropped after he was found dead, hanging in his cell in Tihar Jail here.
The teenager, who may not be named, was tried as a juvenile as he was 17 at the time of the attack. The maximum penalty that could be imposed by the Juvenile Justice Board was three years.
In January, authorities ruled he was 17, citing school records, which shocked the victim's family and others clamouring for him to face the death penalty.
"You may as well set the juvenile free, if the sentence is only three years for heinous offences like rape and murder," said the victim's mother who was in tears after the verdict.
The mother also said she would appeal against the verdict in a higher court.
"I am not happy with this judgment. At least in this case, the juvenile should have been sentenced to life," the victim's brother told Reuters.
The attack - in which the victim was allegedly beaten, raped and tortured with an iron rod by six people on a moving bus in New Delhi - sent thousands of Indians onto the streets to protest over an increase in crimes against women. The woman died from her injuries two weeks later at Singapore's Mount Elizabeth Hospital.
The gang rape case triggered demands from some sections of society to lower the age of juvenile offenders to 16 and to try them as adults above that age.
The government has ruled out lowering the age at which a defendant can be tried as an adult. India's juvenile justice laws have evolved over the past decade and are now in line with UN norms focused on humane treatment of minors.
Delhi gang-rape: Minor gets three years in reform home; family says not happy
The incident occurred in south Delhi when a 23-year-old girl physiotherapy intern was brutally gang raped in a bus that she and her male companion had boarded.Yahoo! India News – Sat 31 Aug, 2013
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