Jonathan Zimmerman is a professor of education and history at New York University. He is the author of "Small Wonder: The Little Red Schoolhouse in History and Memory.”

In 1941, the National Association for the Advancement of Colored People released a report condemning racist school textbooks in New York City. Music books routinely referred to blacks as "darkeys," while literature anthologies called them "coons" or "Sambos." Worst of all, American history textbooks depicted slavery as a genteel institution developed by benevolent white Southerners to "civilize" savage, ignorant Africans.

All of these books were profoundly offensive to the city's African-American population, of course. But they were also full of lies, as NAACP secretary Walter White emphasized. "This study was made not on a basis of racial sensitiveness or pride," White wrote, describing the NAACP's textbook report, "but on the highest plane of historical accuracy and objectivity." Indeed, the report drew on research by pioneering black historian Carter G. Woodson to refute the textbooks' cheery portrait of life under slavery.

I thought of this episode as I read about the furor against Jane Youn, the P.S. 59 school teacher who asked her fourth graders to come up with math problems that drew on their social studies coursework. One of their questions asked how many slaves would remain on a ship, if some of them perished in a revolt; another asked how many times a slave would be whipped over the course of a month, assuming five daily floggings....