I’ve been pondering—and cringing at—a high school memory provoked by the online chatter over the past few days about the imminent publication of “The 1619 Project” in this week’s New York Times Magazine.

I think it happened during my junior year, 1970–71, when an exchange student visited my English class. I don’t remember his name, but he was from South Africa, and our teacher asked him to explain a little about apartheid and how it worked.

“Apartheid”? We-—good (white) college prep students...