Over the last several years, questions have risen across the nation regarding the public school calendar and how to make it a more effective tool for operating schools. These questions are the product of a variety of conditions occurring in states, including a renewed focus on student learning and closing achievement gaps among students, sizable state budget reductions, and scheduling problems due to inclement weather and other disruptive events. These conditions, along with many other circumstances, are considerations lawmakers may take into account as they look at policies to modify school calendars. This report in the SREB Focus series looks at the origins of the 180-day calendar, current instructional requirements in SREB states, opening and closing dates, and recent changes in school calendar flexibility--including the four-day school week and year-round calendar. In 2010, school calendars and calendar policies in SREB states remain relatively unchanged, although a few key differences exist. In some cases, state policy changes offer school districts more calendar flexibility, while other differences reflect a desire for uniformity and consistency throughout a state. (Contains 3 tables.)