An Arizona teacher could face serious time behind bars after she was arrested for sticking a pencil in the butt crack of a 10-year-old student in class.

The alleged incident occurred months ago, on Nov. 28, but parents didn’t learn about it until this week, when prosecutors charged Justine Spitalny Elementary School special education teacher Vicki Biddle Martin with felony aggravated assault on Wednesday, KPHO reports.

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The Cartwright Elementary School District sent a letter to parents about “an incident … surrounding a teacher in which police were involved,” but provided no other details, angering many parents who later heard about the ordeal on the news.

And the details are disturbing.

A police report dated Dec. 13, two weeks after the incident, states “a report was made after the school librarian learned that the defendant, a special education teacher, inserted the eraser end of a pencil in the intergluteal cleft of the 10-year-old male victim.”

The 56-year-old teacher told police the autistic student’s “butt crack” was showing while he was standing at a counter in the library and she made the “very poor decision” to stick the pencil about a half-inch down his pants, KPHO reports.

The librarian told police Martin pulled the stunt twice, though the librarian didn’t catch it the first time.

“(It) makes me feel sad and angry and all kinds of things because how could a teacher do that?” one told the news site in Spanish. “You put your kids in their hands for safety and then they aren’t safe.”

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Other parents seemed more concerned that the school didn’t reveal the incident until months later.

District officials “could have said something sooner,” a parent told KPHO.

None of the four parents approached by KPHO as the picked up their kids at Spitalny Elementary knew anything about Martin’s assault charge.

Officials did not respond when the station inquired about Martin’s employment status, any discipline over the ordeal, or whether she’d had any issues in the past.

The Spitalny school website lists Martin as a “LFI teacher,” which means she works with students with complex cognitive and intellectual disabilities.

The student was reportedly not injured in the incident, though the boy was embarrassed, according to the police reports.

Martin’s aggravated assault charge is a class 6 felony that carries a prison term of 18 months to 3 years for first time offenders, according to Arizona defense attorney James E. Novak.

A KPHO reporter attempted to contact Martin at her home but no one answered the door.