Can a summer camp turn two groups of boys into enemies, and back into friends?

Yes, according to one of the best-known demonstrations in social psychology, though the way it was run is now questioned. In 1954 Muzafer and Carolyn Sherif took 22 boys aged eleven and twelve, who had never met, to a summer camp in Robbers Cave State Park, Oklahoma. The researchers posed as camp staff and quietly watched.

First the boys were kept in two groups that did not know about each other. They hiked, swam and chose names: the Eagles and the Rattlers. Then the researchers brought the teams into contact through a four-day competition with prizes for the winners. The prejudice began as taunting and name-calling, and it escalated to one team burning the other's flag and ransacking its cabin. The groups became too aggressive to control, and the researchers had to separate them. By then, 93 percent of the boys' friendships were within their own team.

Making peace was harder than it looks. Simply bringing the teams together made matters worse. What worked, the Sherifs found, was giving both teams superordinate goals, common goals that could only be reached by cooperating. That reduced conflict significantly more effectively than communication or contact alone.

Today the story is told with more caution. The 1954 camp and an earlier, abandoned attempt in 1953 have come under scrutiny for the way the scientists manipulated and provoked the children, and for possible confirmation bias by Sherif.