In 1965, a 3-year developmental program was begun to determine the desirability of modular scheduling for comprehensive and vocational schools and to investigate the impact of such scheduling on 18 secondary schools. During this time more than 15,000,000 data were provided by the schools. The Stanford School Scheduling System, a computer program for schedule construction based on course design and student course selection, was developed. Over 250 modular schedules have been produced by this program. Some of the findings were: (1) Courses were substantially modified as a result of alternatives provided by modular scheduling, (2) The use of team teaching and large and small group instruction increased, (3) The use of student performance criteria as the basis for advancement increased, (4) Space utilization was different but more space was not required, (5) Disciplinary problems increased and later subsided while attendance problems increased, (6) There was increased interaction between students and school personnel in all schools except one, (7) Staff utilization patterns changed to increased responsibilities but involved less after hours work, and (8) Most students and teachers would prefer not to return to traditional scheduling. Descriptive information for the schools, data tables, and data collection forms are included. (EM)