Debating is a skill that will benefit students for the rest of their lives. It teaches proper ways to argue a point, and requires that students show respect for others' opinions. If you have a controversial topic that you'd like to discuss in class, turn it into a class debate and watch your students flourish.
Discuss the point of the activity. When you decide to hold a class debate, you're really not concerned about the outcome of the debate. You just want students to gain debating skills, patience, research skills and some confidence. Discuss your thinking behind this exercise so that students will understand your purpose and be more likely to want to participate wholeheartedly. Ensure that they know that, even if they have to argue or debate something opposite to their own beliefs, you will still be marking them on effort, not on their argument.
Tell students how they'll be marked. High school students always want to know what's in it for them. So make sure that you go over your marking sheet or rubric with students before assigning the debate topics. Give marks for oral speaking, preparation, research skills, and so on. Make sure that you consult your curriculum for appropriate areas on which to grade your students.
Determine the debate topics. It would get pretty boring if your entire class had to debate on the same topic. So instead, select many different debate topics. Then let students tell you their preferred debate topics. Afterwards, take some time to split the students into debate groups consisting of two sides (pro and con), with 1 or 2 students on each side. Post these groups and topics at least 2 weeks in advance of holding the class debate so that students have time to prepare. (It is up to you whether you give students class time to prepare for the debate and do research, or whether you assign this as an independent project that students must complete on their own time.)
Have the audience help with the marking. A great way to keep the audience interested even though they're not involved in a certain debate is to give them a marking rubric as well. Help them to see what you'll be looking for when it's their turn to debate. But also point out that this is a fair way to teach students to critique their classmate's work. (Understand that student marking like this can never be used to develop a true grade for an assignment. Rather, it should just be an exercise to keep the audience focused and appreciative of objective marking.)
Allow the class debate to take place. Now you're ready for the class debate. Begin with the pro side, allowing them to speak uninterrupted for 5 minutes. Watch for participation from both group members. Then allow the con side to speak uninterrupted for 5 minutes as well. Next, allow time for rebuttals. Give both sides 3 minutes to prepare for rebuttal and then give each side 3 minutes to speak on the comments of the other side (start with the con side this time). You can continue to debate after the rebuttals, but considering the length of the class, you'll probably have to cut the debate short at this point.
Take a few minutes to fill out the rubric for each student, collect the rubrics from the audience, and continue with the rest of the debates in your class.