The educational effects of practical education using a debate exercise are investigated using questionnaires. For the group-work composed of discussion and debate, students understand thoroughly various engineering ethical topics, such as factors preventing ethical decision-making. Students enhance their abilities to make a rational and logical decision by themselves such as a judgment based on correct information. Mutual evaluation by students through group interaction elevates positive educational effects. However, students answer fewer questions related to the understanding of professional duties and cooperate social responsibility because of the group-work using failure cases. Students also show less progress in their abilities to communicate with others and to express their opinions to audiences. A more suitable number of group members solves the latter problem.