(AP) — Kansas City, Kan., police are investigating after a shot was fired into an elementary school as students were preparing to be dismissed.

Police say no one was injured in the incident Wednesday afternoon at Whittier Elementary School. Police believe the bullet came from a drive-by incident about a block-and-a-half away.

The  school was preparing to dismiss students when staff heard gunshots in the neighborhood. The district’s chief of staff, David Smith, said staff made sure all doors were locked and everyone was kept inside.

After about 20 minutes, police told school officials the threat had been cleared and it was safe to dismiss the students.