The injured student is in stable condition at an area hospital, and the suspected shooter is in police custody.
The Mattoon Journal-Gazette reports that the shooting occurred at about 11:30 a.m. Wednesday. Police say after the student was wounded, a teacher subdued the alleged shooter.
All students in the high school were evacuated from the campus and bused to a nearby elementary school.
"We are saddened that this event has happened and we will provide counseling to students in need," the district said on its website. "We will continue to work with emergency personnel to determine what happened.