Washington DC school officials say a staff member who allegedly forced young students to re-enact events from the Holocaust has been placed on leave.
The alleged re-enactment by eight and nine year olds included shootings and digging of mass graves, with one child assigned to act as Adolf Hitler.
DC Public Schools confirmed the incident to the BBC and said an investigation was underway.
In an apology, the school said this was not part of an approved lesson plan.
In an email sent to parents of Watkins Elementary School on Friday, principal Mscott Berkowitz acknowledged "the gravity of this poor instructional decision".
"Students should never be asked to act out or portray any atrocity, especially genocide, war or murder," he said in the email, which was published online by local news outlet Fox5DC.
Mr Berkowitz could not immediately be reached for comment.
Parents quoted by the Washington Post claimed that some children were forced to act as if they were shooting their classmates and pretend they were on transportation trains or gas chambers.
One parent cited by the paper alleged that the instructor told students that the Holocaust took place "because the Jews ruined Christmas".
In a statement to the BBC, DC Public Schools said that the unnamed staff member is on leave pending the results of the investigation.
"This was not an approved lesson plan, and we sincerely apologise to our students and families who were subjected to this incident," spokesman Enrique Gutierrez said.
Mr Gutierrez added that the staff member allegedly used hate speech during the lesson, which he said "is unacceptable and not tolerated at any of our schools".
Several other local schools have recently reported anti-Semitic incidents.
Earlier in December, students at a Washington DC high school, Woodrow Wilson, reported swastikas being painted on a bathroom wall alongside racist epithets.
The case also comes amid warnings from experts about the rise of anti-Semitism in the US.
A report published by the American Jewish Committee in October found that one in four American Jews reported being the target of anti-Semitism in the last 12 months, with the same number saying that they have changed their behaviour because of fear.