Since 1970 the Pasadena Unified School District has operated racially balanced schools under the auspices of a courtmandated desegregation program known as the Pasadena Plan. This report assesses the educational and demographic consequences of four years (1970-1974) of school desegregation. The objectives of the paper are as follows: (1) to provide a detailed report of the levels of achievement in the district's test taking populations after a number of years of desegregation, (2) to provide a comprehensive review of the progression of postdesegregation achievement change for the district's test taking populations, (3) to examine and assess a variety of hypotheses about patterns of achievement decline among the district's test taking populations, and (4) to provide an account of postdesegregation change in the racial and ethnic composition of enrollments in the Pasadena and Inglewood Unified School Districts. Conclusions based on the findings include: (1) desegregation in the two districts studied caused significant decrements in levels of district median achievement, and substantial losses of white enrollment; (2) in the Pasadena district impairment of scholastic performance was singularly in evidence for white students; and (3) the scholastic achievement of the principal minority pupil populations of the Pasadena district was not enhanced by desegregation. (Author/AM)