This report describes a study that investigated the effects of "full-credit semestering" in Ontario secondary schools. In full-credit semestering, the school year is divided in half, and students receive full credit for each course completed each semester. The study also explored the effects of trimestering, half-credit semestering, and mixed organizational models. Eight schools were selected for indepth study using interviews, observation, and records analysis, and additional data were gathered from questionnaires completed by administrators, teachers, and students at 18 other schools. Of 26 schools studied, 20 used full-credit semestering, 2 used trimestering, 2 used half-credit semestering, and 2 used mixed organizational models. Findings showed that the way an innovation was implemented had more effect on staff and student satisfaction than the nature of the organizational change. There was no evidence that students in full-semestered schools achieved better or dropped out less than other students. However, attendance in full-semestered schools was better than the provincial norm, and a significant proportion of students were taking advantage of opportunities to complete their secondary education faster in full-semestered schools. (Author/JG)