At the 1939-1940 New York World's Fair, several thousand boys and girls, all members of a growing national network of high school science and engineering clubs, displayed their science fair projects and conducted live experiments to more than 10 million visitors. Housed in the building sponsored by the Westinghouse Electric and Manufacturing Company, their exhibits depicted a wide range of scientific phenomena. They also represented the conflicting values of science educators and industrialists about the societal worth of science education. In some instances, students' projects and laboratory activities prized hands-on learning and aimed to abet widespread rational thinking for democratic citizenship, which reflected the civic priorities of Progressive science educators. In other cases, science was presented as a magical spectacle with consumer applications intended to entertain and inspire the public's confidence in American industry and scientific experts. Ultimately, the corporate sponsorship of the high school science extracurriculum at the World's Fair marked a turning point when the Progressive purposes of science education began to give way to "manpower" and "professionalist" ends that aligned with the nation's economic and military imperatives. This historical episode also anticipated recent proposals to reform science education in the United States and ideas about scientific learning in museum settings. (Contains 3 figures and 92 footnotes.)