'This model curriculum groups instructional units into three categories. The criterion for these categories is the scale in time, geographical space, and subject matter of the topics to be explored. This system has been designed to guide teachers and students in study of the past on a variety of scales, from broad, global changes to developments that occurred within regions, civilizations, or nations. Teachers may choose to introduce students to an entire Big Era in a few class periods by focusing on the sweeping changes of the era. Or, they may devote a greater number of class days to an era, using several teaching units in all three categories of scale to examine the era in finer detail. Teachers may tailor class time spent on a Big Era to their pedagogical strengths and interests and to state or local content standards. For more discussion of scale in history, see Why an Integrative World History Curriculum in the Foundations of This Curriculum section.'
