Jackson Middle School is the largest middle school in Stark County, Ohio, with approximately 1,400 students and 130 teachers and staff.
His condition wasn't immediately known.
Investigators have not said if the shooting was accidental or intentional.
Jackson Memorial Middle School in Massillon, Ohio.
"UPDATE: JMMS students will be released beginning around 1045AM", the school posted on Facebook. Items found in the backpack could have been used to make an improvised explosive device, police said.
Law enforcement authorities are now working to release students from the middle school. A school official told reporters the town's four elementary schools were closed and the town's high school was being evacuated.
Parents and other family members gathered outside the school as they waited anxiously for their children.
The incident happened at Jackson Memorial Middle School around 7:51 a.m., according to WKYC.
Superintendent Christopher DiLoreto said the school is still considering if classes will continue Wednesday. Many nervous parents waking to see their kids. Extracurricular activities for the day were canceled by the school district. "I just pulled in waiting to hear further information", said Larkins. "'Come get me in, like, an hour".