Students at the Basic Electricity and Electronics School in San Diego were randomly assigned to learning centers with either an 18:1 or 30:1 student/instructor (S/I) ratio to determine the effects on student achievement and instructor performance in an individualized computer-managed course. Data were collected for four months on: (1) student attrition, (2) training contact hours, (3) first-try scores on module tests and phase tests, (4) number of remediations per instructional module, and (5) the number of unsatisfactory scores on practical tests. Observational data were also collected on the frequency and duration of categories of instructor behaviors during the 6-hour computer-managed instructional shift. The larger S/I ratio (30:1) had some detrimental effects on student training time for some career patterns, and on some instructor behaviors. Instructors in the larger ratio condition spent more time in testing and student administration activities, and less time answering student questions on technical matters. The S/I ratio had no significant effect on the student achievement measures. Four references are listed, and appendices include data on student qualifying scores and mean module completion times for individual modules. (Author/BK)