Posted 12:50 p.m. Updated 4:05 p.m.

School officials evacuated an Evanston middle school for three hours Thursday after someone called in a bomb threat, authorities said.

The anonymous threat came in to Chute Middle school, 1400 Oakton St., just before 11:00 a.m., District 65 communications director Pat Markham said.

Chute administrators called the Evanston Police Department and evacuated the school, which more than 500 students attend.

While police with bomb-sniffing dogs searched the school, students went to Dawes and Oakton elementary schools for lunch. Most students were transported by bus, and some walked to nearby Dawes under teacher supervision, Markham said.

The school arranged for the students’ lunches to be transported to them.

At 1:45 p.m., the school received an all-clear and students returned shortly after.

Chute has previous practiced evacuating its students to Dawes and Oakton as part of its crisis plan, Markham said. Thursday’s evacuation went smoothly, she said.

“We did everything necessary to make sure the building was safe for students and staff to return to,” Markham said. This was the first non-drill evacuation of a Evanston middle school in a year and a half, Markham said. In October 2007, Haven Middle School was evacuated after a student brought a fake hand grenade to school as part of a Halloween costume.