On April 5, 1968, Jane Elliott knew she had to do something. The night before, Dr. Martin Luther King Jr. had been shot, and she had to figure out a way to deal with his death and the subject of racism in her third-grade classroom in an all-white small town in Iowa. She came up with an idea that still resonates today.

She separated the kids based on their eye color, blue or brown. She told the brown-eyed kids that the blue-eyed kids were bad, that they couldn’t be friends or play with them. As she continued giving them instructions, the discrimination began almost immediately. Children who had been classmates and close friends started disliking each other and treating each other differently.

Elliott let the bigotry fester until the next day, when she admitted she’d lied. It was actually the blue-eyed kids who were superior and the brown-eyed ones who were bad. In an instant, the prejudices were flipped. Even the test scores reflected the impact of such discrimination — the kids who were told they were bad did poorly, while the superior group did better.

Elliott’s experiment only lasted two days, but she repeated it every year with her new class. In 1985, the PBS series “Frontline” did an episode about her program, “A Class Divided.” In it, several of her former students returned to the school to view footage of how they’d reacted when they were younger, and to discuss how the experiment had impacted their lives over the intervening years.

Elliott also conducted similar experiments with corrections officers and achieved similar results. Now, more than five decades later, she is still doing diversity training and teaching others how to disassemble prejudice in themselves and their organizations.

But you really have to see the way she worked it with her third-graders to understand how authority figures can thrust such hateful ideas into people’s heads at such a young age. These are dangerous beliefs that you aren’t born with — you learn them. Sadly, they have festered in the minds of too many of our fellow citizens for too long.

The saddest part of her story isn’t told in the “Frontline” piece. It was the reaction of the adults in her Iowa town, who shunned her, called her a n***er lover, and stopped being friends with her. Worse, her children were beaten and taunted by other kids who’d been taught to hate her by their bigoted parents.

Do yourself a favor and watch that “Frontline” piece, which is as relevant today as it was long ago…