Nace said she could not disclose the circumstances she believed might have led to his death.
A juvenile petition, or charging document, was filed and the juvenile, 15, was being held in a secured detention center in Harrisburg, Pa., said Angela Krom, assistant Franklin County District Attorney.
Intentionally aiding or soliciting another to commit suicide is a felony of the second degree if the person goes through with the suicide, Krom said. Otherwise it would be considered a misdemeanor of the second degree, she said.
Bonnie Nace said she became worried when her son didn't pick her up at work at 9 p.m. Chad dropped her off and picked her up at her part-time evening job every night, she said.
She called her older son to come get her and they drove to his home, where they learned of Chad's death from the brother of the juvenile who has since been charged, Bonnie Nace said.
Chad Nace was a junior at Shippensburg Area Senior High School and a second-year student at Franklin County Career and Technology Center, where he was studying masonry, his mother said.
"He was an excellent student for us - well-liked, well-respected by the student body. He had many friends and was a nice young man to be around," said Dalton Paul, executive director of the career and technology center.
Most students knew about Nace's death when they got to school Thursday morning, Paul said. Six counselors were available throughout the day to provide assistance, he said.
"Many, many of our students were very upset ... It's a tragedy we never like to hear about," Paul said.
State Police said the shooting was still under investigation.