To illustrate the horrors of slave ships, a middle-school teacher told three black students to lie on the floor and stepped on a girl’s back. The teacher — now reassigned — is white. Most of her students at the Bronx school are black.

Slavery is “hard history,” concludes a new report from the Southern Poverty Law Center (SPLC). Schools don’t teach it well, charges the group, which runs the Teaching Tolerance project.

According to the report, slavery is not a “peculiar institution,” but the “blood-soaked bedrock on which the United States was built,” writes NPR’s Cory Turner.

A survey of 12th graders found that fewer than half knew the Middle Passage — the subject of the Bronx teacher’s lesson — was the brutal trip from Africa to the New World.

“Most alarming,” writes Turner, were the results to a question on why the South seceded:

a. To preserve states’ rights

b. To preserve slavery

c. To protest taxes on imported goods

d. To avoid rapid industrialization

e. Not sure

Perhaps confusing the Civil War with the Revolutionary War, “nearly half blamed taxes on imported goods, Turner writes. Only eight percent chose “to preserve slavery,” which the SPLC considers the correct answer.

(In my day, 50 years closer to the Civil War, historians were split on whether states’ rights or slavery was the most important reason. It was the sort of question a student had to prep to answer on an essay test.)

Textbooks and teachers celebrate heroes who escaped slavery, such as Harriet Tubman or Frederick Douglass, the report says. There’s little about the experiences of enslaved people. It’s easy to teach about white abolitionists and the Underground Railroad, much harder to discuss “the ideology of white supremacy.”

Teaching Tolerance warns against classroom simulations, notes Melinda D. Anderson in The Atlantic.

A class of middle-schoolers in Charlotte, North Carolina, was asked to cite “four reasons why Africans made good slaves.” Nine third-grade teachers in suburban Atlanta assigned math word problems about slavery and beatings. A high school in the Los Angeles-area reenacted a slave ship—with students’ lying on the dark classroom floor, wrists taped, as staff play the role of slave ship captains. And for a lesson on Colonial America, fifth-graders at a school in northern New Jersey had to create posters advertising slave auctions.

Simulating slavery can lead to stereotyping, over-simplification — and angry parents.

Andre Perry recommends reading Born in Slavery: Slave Narratives from the Federal Writers’ Project, 1936-1938 “to learn from those who were enslaved.”