This article provides a systematic analysis of the cognitive processes required for acquiring skill in practical ethical reasoning in a professional domain. We undertook this NSF-supported research project in part to study relationships between case-based instruction in professional ethics and cognitive analyses of ethical reasoning strategies. Using a web-based experimental design, we report striking differences in the students' and ethicists' use of knowledge and reasoning. Virtually all of the ethicists and some students' protocols made significant use of specialized professional knowledge and also used role-specific content in the ethical principles applied in their responses. In contrast, other student protocols made significantly more use of common knowledge and applied more general ethical principles or appealed to consequences in the justification of their responses. Our analyses show how certain strategies were superior to others in regard to identifying alternative moral issues, assessing the moral implications of actions, and providing alternative practical resolutions to conflicts. The findings point to the importance of professional knowledge and role-specific professional obligations in resolving professional ethical conflicts: the same knowledge and "middle-level" principles necessary to comprehend and apply professional codes of ethics.