In a Twitter post on Sunday, Obama said: “Zaevion Dobson died saving three friends from getting shot. He was a hero at 15. What’s our excuse for not acting?”
Obama has lobbied Congress unsuccessfully for tighter gun laws since the deadly mass shooting three years ago at Sandy Hook Elementary School in Connecticut.
Knoxville, Tennessee, police say Dobson, a 15-year-old sophomore, was killed last week as several men went on a shooting spree in the city.
One of the men later died from injuries. Two others were arrested, though one was released after being questioned.
Obama commented during his annual Christmas vacation in Hawaii.