A 15-year-old boy pleaded guilty to attacking teenage girls "chosen at random" as they walked to school in Croydon.
The teenager admitted a string of offences where his victims were either stabbed or sexually assaulted.
Two of the girls, who are not thought to have known each other, were stabbed in the arm and leg. The attacks were linked to four other assaults in the area. Police said none of the injuries were life threatening.
"All the victims were teenage girls, and apparently chosen at random. They were making their way to school when they were subjected to needless and completely unprovoked attacks," said Detective Sergeant Sarah Barrett.
The boy was arrested at home in south London in November last year and was remanded in custody for sentencing on Monday, 7 June.