A Bronx middle-school teacher rattled her students — including one who was near tears — by showing an ISIS video of a terrorist beheading a journalist, documents show.

South Bronx Academy for Applied Media veteran Alexiss Nazario faced termination, but was let off with a $300 fine last summer after acknowledging she made a mistake by not previewing the clip or getting the principal’s permission.

Investigators spoke to three eighth-graders who were freaked out by the macabre clip, which showed a masked man holding a knife to the neck of a kneeling ­victim clad in orange.

The students testified that the video blacked out the actual beheading but showed its gruesome aftermath: the man’s severed head placed on top of his own chest.

“I’m scared at what I just saw. Ms. Nazario showed a beheading video and I was really scared,” one girl told a school staffer right after seeing the clip, according to an ­investigation by the Office of the Special Commissioner of Investigation.

“I don’t even watch scary videos at home,” the girl added.

Another student told probers he lost sleep the night after seeing the video, which had made him feel “uncomfortable.

“It was gross,” he said.

Nazario initially tried to blame the kids by telling investigators one of them had searched for the video on a computer attached to an overhead screen, during a lesson about Iraq, terrorism and ISIS.

Two students told investigators it was Nazario who had cued up the clip.

The technology teacher said the students started “shouting out” that they wanted to watch the video, but acknowledged she was responsible for what happened.

She couldn’t explain why she thought her 13- and 14-year-old students could handle the video, but one recalled her saying, “This is what’s going on in the real world.”

Nazario, a teacher for 26 years whose annual salary tops $105,000, told a different story Friday — telling The Post she had accidentally played the wrong video.

“I was scrolling looking for a specific video. I clicked on the wrong thing. It was a mistake. It was an error,” she said. “I freaked out. I had no idea that was playing.”

Department of Education officials tried to terminate her based on the video and two unrelated charges — but arbitrator Eugene Ginsberg said her years of ­unblemished service merited a lighter penalty.

“This teacher demonstrated a complete lack of judgment, and this incident betrayed our schools’ promise to provide a safe and supportive environment,” said DOE spokeswoman Devora Kaye.

“We sought to terminate this teacher’s employment on the recommendation of the Special Commissioner of Investigation, and ultimately followed the decision of the independent arbitrator.”

Nazario now works as a roving substitute at different schools, ­officials said.