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. A study was conducted to assess the enrollment impact of implementing the lock-out mode; to determine the number and percentage of students not meeting prerequisites by discipline; and to determine which disciplines would be most affected by the implementation of the lock-out mode. Study findings included the following: (1) in fall 1985, 41% of the students did not meet the prerequisites for the classes in which they enrolled, though in spring 1986, this percentage dropped to 31%; (2) lack of basic skills accounted for 61% of student failure to meet prerequisites; (3) computer technology was the discipline that would be most affected by the lock-out mode as 90% of the enrolled students had not met prerequisites; (4) when the prerequisite system was implemented in an informational mode for English classes, English enrollment increased by 18% districtwide; and (5) when the lock-out mode was adopted for English classes, English enrollments decreased by 7%. Enrollment data are appended. (EJV)