Professional education in the medical sciences promotes mastery for eventual career success.  Assessments of student progress should align with mastery.  An educational institution strives to develop and deploy assessments with outcomes that are achievable and consistent with student effort in the curriculum provided.  When the outcomes reflect variability in the assessments of the instructional process, or do not align with institutional goals for students, there are potential adverse outcomes based upon classification error:  failing students who are qualified to advance in their training, or passing students who have not achieved sufficient mastery to move on.  There are challenging problems in dealing with classification error in both knowledge-based and performance-based assessments.  Methods can be developed with policies and procedures to address potential classification error.  This session provides an overview of classification error in student assessment, and will benefit faculty members who administer assessments, assign grades, and/or who are involved in course/curriculum oversight.