Schools often turn to ISM Scheduling Consultants to help design student-centered schedules that support 21st century teaching and learning. The proposed schedule options are always different because of the particular combinations of time, people, space, and program unique to each school. However, certain best-practice recommendations are made to every school; one is the elimination of exam periods (those days when classes stop exclusively for the administration of exams that students take simultaneously and en masse). The traditional exam structure favors the 20th century modality where time is the constant and achievement is the variable. In the 21st century, achievement is the constant and time is the variable.