Police in Portland said they found an exploded device at a playground outside Sitton Elementary School Sunday morning.
Members of the Metropolitan Explosives Disposal Unit said they spoke to a woman who told them her 16-year-old son had used fireworks to blow up his science experiment, The (Portland) Oregonian reported Monday.
The teenager admitted putting the fireworks in a cardboard box with the experiment, the nature of which was not disclosed, and detonating it. He said he didn't intend to damage to school or playground, the newspaper said.
Bomb techs said the device did not pose a threat to the public or property and no charges were filed.