We practiced with several easy topics (Ice Cream: Good) to get students in the practice of forming their opinion. Then I scaffolded it up to have them start brainstorming reasons with like-minded peers. Finally, we spent about 30 minutes debating a few challenging topics. Students were given the topic, had 30 seconds to form an opinion, 4 minutes to put together a logical argument with their group, and then a couple minutes to present it. They were allowed to switch sides at any point.
Our last topic was to decide if ACT and SAT tests should be a factor in deciding college admissions. There were passionate arguments from all sides, including the undecidedes!
The success was this:
After the bell rang, a group of students came up to me on the way out of the classroom. They all started talking at the same time. They were each telling me their idea and asking me for mine. [I almost never give my opinion about topics because it's not my classroom and not my place, it's their classroom.] I stopped all of them and told them that I was proud of them for continuing the discussion, allowing each other to have their say, and forming high quality original ideas. I think it was a success. They were still talking about it on the way into their next class. I love my students!