A 74-year-old substitute teacher is behind bars after a gun in his pocket discharged inside a first-grade classroom Friday.

The incident happened midday at Blountsville Elementary School, said Blount County Sheriff Mark Moon. Blount County District Attorney Pamela Casey said one student was struck by a fragment and checked out by the school nurse.

Moon said the teacher - Henry Rex Weaver – had the gun in his pocket when it discharged. There were students in the classroom at the time.

“It (the sound) alerted administrators,’’ Moon said. “He was detained until we could get him in our jail.”

Moon said authorities are investigating. He is charged with reckless endangerment, third-degree aggravated assault and possession of a firearm on school grounds.

“Obviously I’m concerned about a substitute teacher bring a gun to school,’’ the sheriff said, “and what we can do to prevent that in the future.”

This story will be updated as more information becomes available.