As schools move towards a 21st century model of preparing students for college and a career, it is becoming unnecessary to maintain a system based on time spent in the classroom, according to the report's authors. Rather, learning happens at different times in a variety of settings, and progress should be demonstrated by mastery of content, not merely grade promotion. In the proficiency-based systems examined in "Making Mastery Work", students advance at their own pace as part of a cycle of continuous learning and achievement. This mix of freedom and responsibility is positively impacting both the teaching and the learning at the ten schools studied by Nora Priest, Antonia Rudenstine and Ephraim Weisstein, the report's authors. Issues examined through the collected experiences of the participating schools include: the creation of a transparent mastery and assessment system, time flexibility, curriculum and instruction, leadership for competency education development, and the role of data and information technology in a competency-based education model.