The victim, Cornelius German, was shot to death in a backyard less than four blocks from President Barack Obama's Kenwood home, police said Tuesday.
German, a freshman at Kenwood Academy, was found unresponsive around 9:40 p.m. Monday. He had been shot in the back and was pronounced dead at the scene, police told The Associated Press.
Investigators say they believe the incident is gang-related. German's mother says her son was not involved in gang activity, he just wanted to hang out with older boys.
Before the shooting, German's mother says, her son called to ask for a ride home. When she arrived to pick him up, police were already on the scene and told her a boy -- her son -- had been shot.
"I heard some of the guys say 'they just shot my little homie,' " said Timika Rutledge-German, Cornelius's mother. "He wasn't the intended target."
Chicago police say they had no suspects in custody as of Tuesday afternoon.
German's death comes about three months after the fatal shooting of another 15-year-old, Hadiya Pendleton, who was gunned down in a park about a mile from the Obama home.
Police spokesman John Mirabelli said the motive in the latest shooting death was not known.
The mother was told by friends that her son was leaving a dice game when he was shot. Police did not confirm that.
The Associated Press contributed to this report.