How to Teach Using Individual Role-Playing Exercises
More about Context and Roles
If this is a stand-alone written exercise, you can assign a single character to all of the students, which means you'll have only one kind of paper to grade. For a controversial issue, it is possible to assign several characters and to have the student research and write about each of them. If they are giving presentations, it will be much more fun if they all have different characters.
More about Introducing the Exercise
Even if students are familiar with the idea of interactive role-playing, they may be confused about the idea of writing in character and may need help understanding the character they've been assigned and what they are expected to tell you. Another important issue is: who is the audience for the letter/speech/problem statement/etc. that the student is supposed to produce? What is their interest in the problem and how much science background do they have? How much time will they give the student's character? That last question gives the instructor an excellent and realistic excuse to assign a maximum length to the project.
More about Student Preparation and Research
Since the students are on their own, unless the topic is a simple one with few resources needed beyond their textbook and possibly the Internet, they may need some direction about which questions to work on and if their character(s) may choose to deal with them differently than the students themselves.
More about the Concluding Discussion
It is worthwhile to have the student step back from the character at the end of the exercise and tell you what they personally think about the problem and the character. This can be handled in writing or as part of a class discussion. If the students had different characters, what did they think about each others' characters and their part in the problem?