Police sources say the discovery was made by an exterminator at the school who smelled a foul odor and called 911.
President Trump initially blamed Iran for the attack, later said he wasn't certain who was to blame, and then said he would accept the results of the Pentagon's investigation.
It appears the fire started in the library, which sustained significant damage.
President Donald Trump said on Monday he doesn't "know enough" about the strike on an Iranian elementary school that Iran says killed at least 168 people.
A newly surfaced video appears to show a U.S.-made missile hitting a building in Iran adjacent to a girls' school where local officials say 168 people were killed.
Some critics are calling for the parent to be fired from her job in education.