The teacher who conducted the lesson was fired. (Representational)

A New York teacher singled out African-American students and cast them as slaves in a mock "auction" as part of a social studies lesson in March, a media report said.

The incident happened in two fifth-grade social studies classes at The Chapel School -- a private school in Westchester County -- about 15 miles north of mid-town Manhattan, CNN reported on Thursday.

The teacher reportedly asked all of the African-American students in each class to raise their hands and then instructed them to go stand in the hallway, where the teacher placed imaginary chains on their necks, wrists and ankles. Those students were then instructed to walk back into the classroom and line up against the wall.

The teacher then proceeded to conduct a simulated auction of the students in front of the rest of the class, apparently in an attempt to depict the sale of enslaved Africans to white plantation owners that happened in the 18th and 19th centuries.

The teacher who conducted the lesson was fired.

An investigation by the New York Attorney General's office found that the re-enactment had a "profoundly negative effect on all of the students present -- especially the African-American students".

"Every young person -- regardless of race -- deserves the chance to attend school free of harassment, bias, and discrimination," Attorney General Letitia James said in a statement on Thursday.

"Lessons designed to separate children on the basis of race have no place in New York classrooms, or in classrooms throughout this country."

As a result of the investigation, Letitia James announced that the school would have to make significant changes to the way it approaches diversity and inclusion, which includes hiring a chief diversity officer, increasing minority representation in the faculty and committing new financial aid to increase diversity in the student body.

The school said in a statement that it has agreed to comply with the changes.

The Chapel School serves 240-320 students each year from preschool through eighth grade, according to its website. In its statement, the school said 43 per cent of its students were minorities.