This brief highlights the importance of using a measure like chronic absenteeism, rather than average daily attendance, in order to identify concerning patterns in elementary attendance rates. The chronic absenteeism measurement is better able to shine a light on the number of individual students struggling with attendance. Subsequent briefs in this series will examine the implications of chronic absenteeism for students and highlight different ways schools can use data to identify and support these students. [For "Connecting Attendance and Academic Outcomes. Chronic Absenteeism in Oregon Elementary Schools. Part 2 of 4. September 2016. Research Brief Series," see (ED578928); For "Daily Attendance Data. Chronic Absenteeism in Oregon Elementary Schools. Part 3 of 4. September 2016. Research Brief Series," see ED578929; For "Excused and Unexcused--The Value of Labeling an Absence. Chronic Absenteeism in Oregon Elementary Schools. Part 4 of 4. September 2016. Research Brief Series," see ED578930.]