In 1968, Jane Elliott was just another American schoolteacher. She taught third and fourth grade (eight to nine-year-olds) children at a school in Riceville, Iowa, which was a very typical, all-white, small American town.

Jane had tried to introduce her students to the idea of racial equality. She had even appointed Martin Luther King as the class's 'Hero of the Month', but she struggled to explain what racism was really like to the all-white class. They seemed keen to learn, but had never seen a black person in real life.

After the assassination of Martin Luther King, Jane tried a more direct exercise to bring the truth home about racial discrimination. It was an exercise which was to change her life.

Jane Elliott told her pupils a pseudo-scientific explanation of how eye colour defined people: blue eyes showed people who were cleverer, quicker, more likely to succeed. They were superior to people with brown eyes, who were described untrustworthy, lazy and stupid . She then divided the class according to who had brown eyes and who had blue eyes. To ensure clarity of divisions - given that some eye colours might be subject to dispute, she used ribbons to mark out the 'inferior' brown-eyed children (those with clearly different eye colours acted as bystanders). To reinforce the situation, she gave the superior group extra classroom privileges, and would not let the brown-eyed children drink from the same water fountain. She made a point of praising the blue-eyed children, and being more negative to the browns.

Jane Elliott was amazed at the speedy transformation in her class. The superior blue-eyed children became arrogant, and were bossy and unpleasant to their brown-eyed class mates. The brown eyes quickly became cowed and timid, even those that had previously dominated the class. But what really astounded Jane was the difference academically. Blue-eyed children improved their grades, and managed mathematical and reading tasks that had proved out of their grasp before. Brown-eyed high-flyers stumbled over simple questions.

A few days later, Jane Elliott told her class that she had the information about melanin the wrong way round, and swapped the colour superiorities over. The brown-eyed children tore off their now-hated ribbons, and the situations quickly reversed.

Jane Elliott had proved - more dramatically than she had ever thought possible - how much discrimination is soaked up subconsciously, by both the oppressor and the oppressed. She had not told her pupils to treat each other differently, only that they were different; and yet they developed the characteristic responses of discrimination. Jane Elliott felt that they did this because they had already absorbed discriminatory behaviour from their parents and other adults. On the plus side, she had also proved that racism can be unlearnt as quickly as it can be learnt. She had also found an excellent way of demonstrating what it feels like to be the subject of discrimination.

Jane's exercise - which she repeated with subsequent classes each year - did not make her popular with many of her neighbours. Her family was victimised, and her father forced into bankruptcy. Parents would refuse to have their children taught by the 'n****r-lover'. For much of the time she had the support of her superiors in the education system, so that as news of her exercise spread, she was able to appear on television shows, and even start to repeat the exercise in professional training days for adults.

But by the 1980s, her bosses felt they could no longer support her dual roles by providing unpaid leave, and she left school-teaching to become a full-time 'diversity trainer'. She took the Brown Eyes/Blue Eyes exercise, and other work, out to colleges, and government, professional and community groups across the world. In these training sessions, she usually puts the brown eyed attendees in the superior position. As these groups are more likely to be mixed race, this ensures that the people feeling the discrimination are more likely to be white, who are less likely to be used to it. She uses choice of language and tone, removal of basic rights (such as being allowed to speak without permission) and a constant shifting of rules to discomfort the blue-eyed participants. At the same time she uses positive language, praise and encouragement to the brown-eyed people. Even assertive, intelligent professionals have expressed their surprise at how quickly they start to mirror the trainer's behaviour, and how thoroughly they become affected by this technique, even at a two hour seminar. Jane Elliott then hammers home the point: people who are the subject of real discriminations cannot call a halt to the misery and frustration at the end of the afternoon. Jane Elliott started her exercise to point out racial discrimination: now she uses it to highlight sexism, ageism and homophobia too.

And what of Jane Elliott's original classes? These children had gone home after the exercise and told their parents that racism was wrong, and it was a lesson that stayed with them. Reunions and interviews have shown that the children remember the exercise and are positively affected by it, feeling that it makes them more empathic and sensitive.