Final answer:
Reducing prejudice is effectively achieved by encouraging cooperation and common goals among groups, exemplified by Sherif's Robbers Cave experiment and the jigsaw classroom technique.
Step-by-step explanation:
An effective way to reduce prejudice according to the study by Sherif at a summer boys' camp is to encourage cooperation and common goals among groups. This was illustrated by Sherif's Robbers Cave experiment where the introduction of superordinate goals that required cooperative effort led to a reduction in prejudicial attitudes among opposing groups. Similarly, the jigsaw classroom technique also promotes cooperation among diverse students to achieve a common objective, leading to a decrease in prejudice.
Such cooperative strategies and settings that involve equal standing, shared objectives, and institutional support have been shown to be instrumental in reducing negative attitudes and fostering positive intergroup relationships. Therefore, interventions that promote interaction and collaboration on common goals can be significantly effective in decreasing prejudice and discrimination in various settings such as schools and the workplace.