The lockdown at West Middle School in Martinsville was ordered after the 7:30 a.m. shooting, the Indianapolis Star reported. Many parents had been waiting anxiously outside the school while it was still under lockdown.
A suspect who was arrested several miles away from the school may face a charge of attempted murder, police said. Investigators said they found a handgun on a hillside near the school.
The wounded boy was identified as Chance Jackson, 15. Sgt. Curt Durnil of the Indiana State Police said he was in critical but stable condition at Methodist Hospital in Indianapolis.
The boy was airlifted the 30 miles to the hospital and had surgery there. His family released a statement asking for privacy and thanking well wishers for their prayers.
Police said the alleged shooter was suspended about a week ago. Investigators did not say why he was disciplined or speculate on a motive.
He had not been identified or formally charged Friday afternoon.