Fourth-graders at Flowery Field Primary School walked into a murder scene when they came to class Tuesday – blood smears, a body outline taped to the floor, an overturned table and police tape.

Dozens of 8- and 9-year-old detectives processed the scene with “official police evidence forms” and investigated the apparent “elf murder” as part of an “engaging and exciting” writing project, officials told the Manchester Evening News.

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But parents contend their children were traumatized by the “extreme” lesson and suffered from nightmares.

“There was police tape and a table had been knocked over, and there was blood smeared on one of the tables,” said a mother who did not want to be identified. “The idea was Elf had been murdered by another Elf. My daughter came home and she was absolutely traumatized.

“I’m not the only parent who felt like that,” she said. “A lot of the kids in Year 4 were unsettled by it. I’m very open with my children and I understand you can’t protect them from everything. But my child was very upset last night and had to sleep in my bed.”

Pictures of the assignment posted to the Flowery Field Twitter page showed students came across a bloody elf hat, and writing on a window that read, “I hate Christmas” – clues designed to lead students to the culprit.

“Year 4 writing detectives are on the case!” the post read. “What has happened in 4VS today? Collecting as many clues as we can find.”

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Headteacher Ian Fell defended the assignment, alleging “the children were all excited and they really did buy into it.”

“One of the children said to me ‘I am definitely being a detective when I grow up,’” Fell told the Evening News. “Of all of the 90 children who took part, none of them showed anything but full engagement.

The school’s Twitter account later posted updates about fingerprinting suspects, as well as journalism and math projects centered on the case.

“I have been a teacher for 30 years and this is, in my judgement, an appropriate, engaging and exciting thing that children eight and nine have done. They have been so up for it,” Fell said. “I’m really looking forward to see the equality of the outcomes.”

Several folks who commented online were less impressed.

“And people wonder why children have become so desensitized that they bring a gun to school and murder their classmates,” Tina posted to Twitter. “Only in today’s world does a teacher use murder to teach eight and 9-year-old children.”

“Murder is not an appropriate subject for little kids. Real life murder is horrific,” Christine Wagner wrote. “Plenty of time in college to opt for a Forensic Science major. Your teacher = morally skewed and so = your administration for allowing this.”

Others with children who went through the assignment defended the school.

“Can I ask how this exercise is ruining kids? My son took part in this 2 years ago and was so engaged and excited to discover the outcome,” Sarah Forrest posted. “It involved teamwork, investigation and most importantly fun amongst peers and teachers.”

Forrest pointed out “children their age and younger are at home playing games like Call of Duty and Fortnite, actively ‘murdering’ in these games!!

“They see and hear worse on the evening news,” she wrote.