Get students primed for the real thing by staging a large-scale debate and using fairy tales as the subject matter. Instead of students facing the pressure of one-on-one debating in front of an audience, divide the class into two large groups. Make a debate resolution from a fairy tale, such as, "Be it resolved that Goldilocks was justified in eating the youngest bear's porridge." Line each group up facing each other. Have the first student on team one make a point. Ask the first student on the other team to rebut. Continue in this manner down the line by alternating teams as players rebut the previous point.
This game helps students think carefully before they make an argument or rebuttal. Assemble a large number of index cards and write "Comment" on half and "Question" on the other half. Distribute one of each card to the entire class. Put a debate topic or resolution on the board. Students must raise their hand and cash in the appropriate card to make a comment or question. Students will learn to keep their cards for when they have a very important point to make. You can reward players with extra cards for making excellent points or asking important questions.
You can use games to teach students to make a quick argument on the fly. Break the class into two teams, "For" and "Against." Have the "For" team sit in an outward-facing circle. Have the "Against" team sit in a larger inward-facing circle, with each member facing a member of the opposite team. Have a variety of debate topics or resolutions on small slips of paper in a hat. Draw one randomly and have members of the "For" team make arguments to their counterpart in one minute. Have members of the "Against" team rebut in one minute. Have one circle rotate and draw a new topic from the hat.
You can use online tools to teach students the basics of debating. Funenglishgames.com hosts a debating game that is perfect for younger children. Students choose from a variety of topics. A character in the game argues for or against a resolution and students must rebut by selecting one of four arguments listed. The game then "votes" on whether the argument was convincing or not. The game teaches students to choose the strongest argument available.