Authorities provided little information about the circumstances surrounding the bloodshed and took no questions from reporters at a news briefing following the shooting, Reuters reported.
The two victims were gunned down at about noon on a sidewalk near the front entrance to the South Education Center in Richfield, Minnesota, a city of about 37,000 people adjacent to Minneapolis, police chief Jay Henthorne told reporters.
The victims, both enrolled as students, were taken to an area hospital, where one died of his injuries and the other was listed in critical condition, Henthorne said.
The Minneapolis Star-Tribune, citing friends and relatives, identified the slain youth as 15-year-old Jahmari Rice, who was living with his grandmother. According to his former football coach, Tuesday was Rice's first day of classes at the South Education Center.
The suspects made a quick getaway after the shooting, Henthorne said, without offering any information about how many assailants were at large or the motive.
Police searched the school and surrounding area and "determined that no further threat existed" before lifting a precautionary lockdown of the education center and other schools in the vicinity, the chief said.
The police department later issued a statement online saying that two suspects in the shooting were taken into custody, and a pistol was seized, as authorities served search warrants on two Minneapolis addresses.
Police gave no further details about the investigation except to say that no additional suspects were being sought.
The Richfield school center provides special educational programs for about 200 students ranging in age from pre-kindergarten through 21, according to Sandra Lewandowsky, superintendent for the area school district.
Television station WCCO reported that the school was placed under lockdown in September after a student was found with a handgun. That student was taken into custody and nobody was hurt, WCCO said.