As part of an ongoing effort to understand the nature of student performance and persistence at Southwestern College (SC), a study was conducted in fall 1976 to determine the effect of reading ability on student course performance. An analysis of the Nelson-Denny Reading Test (NDRT) scores of 4,610 students revealed that, on an average, students scored at the 13th grade level, though 23% had reading scores at or below the 9th grade level. When reading levels were compared with course completion rates and grade point averages, it was shown that student performance was related to reading ability in 80% of SC's academic departments, and that reading ability was especially critical in Behavioral Science, Business, English, Life Science, Mathematics, Paramedical Studies, and Social Science departments. Student performance was affected by reading ability in 93% of all subject areas and in 45% of all courses. Based on study findings, the implementation of a Course Reading Index Prerequisite System was recommended, which would limit course enrollment to students reading above a specified level. The study report contains an analysis of the likely effects of the proposed Prerequisite System; and information related to SC's Predictability Counseling program, which provides students and counselors with information on probable success for various student objective categories and majors, and on chances for success in specific courses based on NDRT scores. (DAB)