Students of this age are often concerned with what is 'right' and sometimes have very strong, apparently fixed ideas about things. You can ask students to prepare an argument in favour of or against something so that they are forced to think about the other side of an argument. Class discussion can then take the form of a debate between opposing sides. Beyond that, students may lose interest or the discussion may lose its focus. With a clear, concrete focus, students can work briefly in small groups.
Some groups can then offer feedback to the whole class.