This paper explores the reasons for the rapid adoption of intelligence tests by the public schools, and the historical relationship between testing and ability grouping or tracking. Case studies are presented of three California communities--Oakland, San Jose, and Palo Alto--between 1910 and 1925. These communities have been selected because they were pioneers in the use of intelligence tests; because they were associated with Lewis Terman and Stanford University; and because they were representative of urban communities in terms of size, socioeconomic status, and ethnic diversity (including large immigrant populations). Reasons for the rapid emergence of intelligence testing are suggested, followed by a review of Lewis Terman's work and philosophy. The case study of the Oakland schools describes the efforts of John W. McClymonds, Vinnie Hicks, Ellwood P. Cubberley, Fred Hunter, and Virgil Dickson. The San Jose case study describes the work of Kimball Young and Walter L. Bachrodt. The testing done by William V. Proctor is described in the case study of Palo Alto. These histories are said to support the suggested reasons for the rapid adoption of intelligence testing: testing technology, educational problems of the time, and social values which supported efficiency in tracking. (GDC)