This study by the San Diego Community College District (SDCCD), California, aims to determine the impact of prerequisite enforcement on retention and course completion rates in English and math courses among underrepresented students. The report analyzed a subset of the more than 300 prerequisite-enforced courses offered by the SDCCD. The course selection criteria included: (1) all English and math courses with 30 or more enrollments for at least one underrepresented ethnic group; and (2) courses in other subject areas that were identified in a previous study as having a statistically significant change in course success rates. Data from selected courses were broken down by ethnic group and examined for changes in course enrollments and success rates, term retention rates, and term-to-term persistence rates. Immediate and long-term effects were assessed, using data from fall 1996 through fall 2001. In terms of the impact of prerequisite enforcement, all of the ethnic groups with the exception of Filipinos showed a decrease in term-to-term persistence rates across all multi-year comparisons. Furthermore, a majority of these decreases were found to be statistically relevant. The decrease was determined to be inconclusive, however, as it could be the result of an increase in the number of students achieving their educational objective. (Contains 67 tables and 2 charts.) (NB)