In the San Jose/Evergreen Community College District in California, prerequisite levels have been established for almost all courses offered, though students may insist on taking classes above their prerequisite level. In an effort to validate the district's prerequisite system, a study was conducted comparing academic success rates of students who met all prerequisites before taking higher level courses in fall 1991, with success rates of students who took courses above their prerequisite level from spring 1989 through fall 1991. Results of the study included the following: (1) the overall success rate for all disciplines among students who met their prerequisites in fall 1991 was 67%; (2) the overall success rate for the 7,261 students who took courses above their prerequisite level was 50%; (3) students meeting all prerequisites had a 28% better chance of success than those taking courses above their prerequisite level; (4) for the 38 disciplines which had 30 or more students taking courses above their prerequisite level, 94% showed higher success rates for the students meeting prerequisites than those not meeting the prerequisites; (5) an analysis of the 38 disciplines indicated that meeting prerequisites was as important to student success in vocational courses as in nonvocational courses; and (6) of the 38 disciplines, only two revealed a small negative correlation between student success rate and having met prerequisites, while four disciplines showed negligible correlations between prerequisite completion and success. Detailed data tables, with results by discipline, are included. (PAA)