One of the most difficult parts of debating for both native speakers and ESL students is rebuttal. From my experience the rebuttal part for Japanese ESL learners is especially hard since debating is not something that they commonly do even in Japanese. The most important aspect is providing them with a structure to follow. 

To rebut effectively in English debates, here are some essential tips:

Active Listening: Understand your opponent's arguments by actively listening and taking notes.

Preparation: Anticipate your opponent's points and prepare your arguments in advance.

Signposting: Structure your rebuttal by starting with an acknowledgment of the opponent's point.

Address Key Points: Focus on the most crucial aspects of your opponent's argument in your rebuttal.

Provide Evidence: Support your counterarguments with facts, statistics, or examples.

Expand Vocabulary: Enhance your English vocabulary to express your ideas more effectively.

1. Start with Basic Topics

Begin with simple, relatable topics that ESL students can easily understand and express opinions about. Gradually progress to more complex subjects as their language skills improve.

2. Emphasize Vocabulary

Introduce debate-specific vocabulary and phrases, such as "opening statement," "rebuttal," and "counterargument." Encourage students to incorporate these terms into their speeches to enhance their language proficiency.

3. Provide Structured Practice

Break the debate process into manageable steps. Teach students how to outline their arguments, provide evidence, and refute opposing viewpoints. Practice each step separately before combining them into full debates.

4. Foster a Supportive Environment

Create a safe and inclusive classroom environment where ESL students feel comfortable expressing their opinions and making mistakes. Encourage peer feedback and constructive criticism.

5. Incorporate Technology

Use online resources, debate platforms, and multimedia materials to make learning engaging and interactive. ESL students can watch and analyze debates in English, helping them grasp the art of persuasion.

6. Encourage Research

Encourage ESL students to research thoroughly before debates. This not only improves their argumentation skills but also enhances their knowledge of the topic.

7. Practice, Practice, Practice

Regular practice is key to mastering debate skills. Host mock debates, organize debates within the class, or even encourage ESL students to join debate clubs or competitions outside of school.