HERMON – The school department is investigating an incident in which a Hermon High School student reportedly threatened a girl on the school bus with a pocketknife.

A boy pulled out a knife on the bus ride home on Tuesday, sliced open a water bottle and told a girl, “This could be your head,” according to Sgt. William Laughlin of the Penobscot County Sheriff’s Department.

An informational report was taken, but no charges have been filed and the school is handling the situation, Laughlin said.

The girl’s mother, Eva Cookson of Carmel, notified police.

“A student, at this point, has been disciplined,” Hermon High School Principal Brian Walsh said Thursday. “I think the school has taken appropriate action.”

Further disciplinary action and an expulsion hearing are probable, Walsh said.

The 14-year-old girl told her bus driver what happened and was crying when she got off the bus, her mother said.

“She was pretty scared,” said Cookson, who has three other children who ride the same bus. “I wanted to know if he was going to ride the bus [Wednesday] with my kids.”

School officials met with Cookson on Wednesday, but said they could not tell her how the boy, who is 16 or 17, has been disciplined because of privacy requirements, Cookson said.

“Parents need to know what’s going on,” she said. “I want him expelled.”

The boy has not been on the bus since Tuesday, Cookson said. She was given that information by her daughter.

She is also concerned because the boy, who her daughter describes as a “bully,” likely had the knife on him while in class at the high school, Cookson said.

Students are not allowed to have weapons, even toy replicas, in their possession at any time while on school property, according to the Hermon school department code of conduct. Such violations warrant discipline ranging from suspension to expulsion, the code says.

Expulsion requires investigation of the student’s behavior by the entire school committee, not just the superintendent or one committee member, according to the code.

The next meeting of the school committee is scheduled for Jan. 24.

For now, Cookson said her daughter is relieved not to see the boy on her way to and from school.

“She’s just so glad he’s not on that bus,” Cookson said.