A 15-year-old boy was shot outside his Brooklyn high school Tuesday afternoon, cops and law-enforcement sources said. 

The boy was blasted in the right leg by an apparent other teen around 2:40 p.m. in front of South Shore High School on Flatlands Avenue in Canarsie, according to authorities and sources. 

The victim started running away after the shooting before collapsing nearby, sources said. 

Officers responded to the intersection of Glenwood Road and East 58th Street, a short walk from the public school, cops said. 

The boy was taken to Brookdale University Hospital Medical Center, where he was listed in stable condition, authorities said. 

The shooter, also believed to be a male teen, fled on foot, police said. 

The motive for the violence was unclear by the early evening. 

The school does scan its students for weapons, sources said. 

The shooting comes three days after 17-year-old Sincere Campbell was fatally shot in an early-morning Bronx attack, cops said. 

Campbell took a bullet to the stomach on Evergreen Avenue near Westchester Avenue in Soundview – down the block from his home – around 3:25 a.m. Saturday, police said. 

He was rushed to Jacobi Medical Center, where he succumbed to his injuries, cops said. 

The shooter took off in a black sedan, authorities said. 

The motive for the slaying remained unclear Tuesday. 

On Thursday, another 17-year-old boy was shot in the leg near a Staten Island high school, cops said. 

The boy took the bullet around 1 p.m. outside Ralph R. McKee Career and Technical Education High School in St. George, police said.

He was rushed to Richmond University Medical Center, where he was listed in stable condition, cops said.