In response to the Every Student Succeeds Act (ESSA) (2015), 36 U.S. states have adopted chronic absenteeism as an indicator of school quality and student success. It is also being increasingly utilized within schools to identify students at risk for future educational problems, as research consistently shows that early absences are related to later achievement issues. By leveraging readily available attendance records, schools can identify students at risk of poor outcomes early in their educational lives and provide them with supports before challenges worsen. Despite its pervasive use, major theoretical assumptions underlying this indicator have never been validated. The current study represents the first empirical test of the most basic assumption of chronic absenteeism--that all absences from school are equally useful in providing diagnostic information to determine future risk status. To test the diagnostic utility of different absence types across the early elementary grades, this study employed ROC analyses with administrative data from a large, urban school district. Findings indicate that only unexcused absences provide diagnostic accuracy in determining future achievement status in the early elementary grades, whereas excused absences provide no diagnostic accuracy and actually dampen the ability of unexcused absences to determine students' achievement risk status when used in conjunction with them. These results have implications for researchers, policymakers, and practitioners and necessitate additional empirical studies that test the underlying assumptions of chronic absenteeism to ensure that it is being used both effectively and ethically in the early identification of at-risk students.