Evaluations are practiced in political contexts, posing ethical dilemmas to evaluators. It is important, therefore, to prepare evaluation students for ethical decision-making in their future evaluative work. This study explores the use of scenario-based moral reasoning and ethical argumentation as an instructional strategy for teaching evaluation ethics to a group of graduate students enrolled in an online course on program evaluation. The participating students were asked to discuss an ethical scenario in an asynchronous online format during five consecutive weeks. The results suggested that participation in this assignment benefited students in three main ways: (1) providing new insights and adding new perspectives, (2) recognition of and discussion on dichotomies, and (3) attending to one's own and others' unwarranted assumptions. Furthermore, we identified some of the students' ethical misconceptions regarding evaluation and were able to relate these misconceptions to Bandura's theory of moral disengagement and Sartre's notion of "self-deception" or "bad faith." Implications for teaching evaluation ethics and suggestions for future research will be presented and discussed.