This digest discusses the rationale for changing school calendars. It describes what some districts are doing and advises school leaders and board members on the issues that typically arise when a calendar is changed. It examines the nationwide push toward a longer school year, driven in part by so-called high-stakes testing and mandated increases in instructional hours. The digest also looks at the district and state levels and how their calendars are being adjusted in response to local imperatives. In Michigan, for example, district superintendents had to incorporate a state-required increase of 108 instructional hours. While some year-round schools offer intercessions during breaks for students who need remedial help, other districts are exploring extra days, after-school programs, and/or summer sessions as ways to extend learning. Researchers and educators recognize that the traditional school calendar does not correlate with children's learning patterns. However, experts agree that it is of little value to add days to the calendar without a concrete plan for using the time to enhance instruction. Viewed this way, the calendar becomes a variable that educators can tailor to the particular needs of their students; modified and extended calendars are rapidly becoming the norm in schools across the country. (Contains 14 references.) (RJM)