A valid screening system requires a screener that accurately predicts whether or not students are at risk given their current performance. To understand a screening measure's accuracy, predicted student performance data (i.e., screening data) must be compared with actual performance data. When these sets of data are compared in a setting where interventions are in place, measures should be taken to ensure that the effects of interventions are controlled in the student data. This brief discusses screening assessments and describes classification accuracy. Understanding classification accuracy will help practitioners become more discerning consumers of screening data.