An aide for Sen. Hillary Rodham Clinton gave a Grinnell College student a question to ask the Democratic presidential candidate during a forum this week in central Iowa.
The campaign did not mention at the event that the question had been planted, and it initially denied the incident.
"This is not standard policy and will not be repeated again," the campaign said in a statement Friday that admitted the incident.
Clinton's aides said the senator did not know the question had been planted when she called on the student. "The senator had no idea," Clinton spokesman Mo Elleithee told The Associated Press.
Clinton appeared Tuesday at a biodiesel plant in Newton. The student, Muriel Gallo-Chasanoff, later told Grinnell College's student newspaper that she was asked by a senior Clinton staffer to pose a question about global warming and that staffers prompted the senator to call on her, the newspaper reported.