UPDATE (WKOW) -- Students are returning to the Sauk Prairie High School after police finished a search of the building.
The Sauk Prairie Police Department told 27 News a sweep of the high school did not find a bomb.
Authorities wrapped up their search just before 1 p.m. Tuesday and are allowing students to return to class.
PRAIRIE DU SAC (WKOW) -- Administrators evacuated the Sauk Prairie High School after receiving a bomb threat Tuesday morning.
In a letter to parents, the district said a person called in the threat just before 11 a.m.
The caller said the bomb would go off in one hour. Administrators called authorities before deciding to evacuate the high school and send students to the middle school.
The letter said the decision was made so that law enforcement could "conduct a thorough search of the building."
Staff stayed with students to "ensure their safety and well being."
The district asked families not to go to the high or middle schools to allow authorities to "focus on securing the buildings."