In fall 1985, a computerized prerequisite checking system was implemented in the San Jose/Evergreen Community College District (SJ/ECCD) featuring an informational mode, which provides information about whether a student meets a prerequisite, and a lock-out mode, which prevents a student from registering for classes if prerequisites are not met. The system was in an informational mode for all courses for fall 1985 and spring 1986, and began implementing the lock-out mode for English in fall 1986, and for English as a Second Language in spring 1987. In summer 1987, a study was conducted to choose additional disciplines for the lock-out mode. Study findings included the following: (1) as course prerequisites were increasingly enforced and as available data became more accurate and complete, the total percentage of students not meeting prerequisites decreased from 41% to 31% to 24% to 15% between fall 1985 and spring 1987; (2) disciplines with complex prerequisites or in which students could easily by-pass advisory prerequisites anticipated the greatest impact; (3) of the disciplines scheduled for lock-out in fall 1987 and spring 1988, the disciplines with the greatest percentage of students not meeting prerequisites in spring 1987 were Construction (57%), Laser (32%), Nursing (30%), and Drafting (28%). (EJV)