Totino-Grace students were evacuated from the Fridley school Friday but told to remain on campus after a thermometer was discovered on the floor of a classroom, the Star Tribune said.
A hazardous materials assessment team and the Minnesota Pollution Control Agency's emergency response team remained on site more than two hours after the school was evacuated.
Students were told to remain on campus, because there appeared to be no health hazard.
Students were told to stay put in case chemicals were found on shoes or other items.
Parents were alerted by phone and e-mail, and the school's website was posting continuous updates.