Divorcing the mechanics of public speaking from the work of delivering a graded speech can help build students' skill levels in a low-stress environment. Set aside regular classroom time for group speaking practice. Use assignments that isolate skills like voice projection, varying inflection or speaking from notes. For example, one week students could take turns reading a short paragraph with the goal of only looking at the paper once per sentence. Another week they could take turns reciting short, silly poems from memory, or choosing the best gestures to emphasize various sentences.
Providing a safe setting for practicing a persuasive speech can both improve your students' speaking skills and help them internalize the importance of practicing before the final delivery. If students have a long-term persuasive speaking assignment, create a schedule of practice sessions in which they can deliver rough drafts or sections of their speeches, then provide feedback that will help them polish the final products. Another activity is to assign short, frequent persuasive speaking assignments to build up each student's familiarity with the process of composing and delivering a persuasive speech.
When a student watches or listens to a recording of her own speech, it can help her develop a more accurate impression of where she can improve. Ask each student to create and evaluate a video recording of herself delivering a persuasive speech. Provide a checklist or questionnaire that will guide the student through an evaluation of her physical demeanor, vocal delivery, persuasiveness and factual accuracy. Have each student choose one element at a time to try to improve in time for the next self-evaluation.
An important part of persuasive speaking is the ability to understand and interact with other points of view. You can help students develop this skill by training them to give constructive feedback on their classmates' speeches. One way to do this is to provide a few minutes after each talk for the class to ask questions or give suggestions regarding the speaker's technique or content. Another way is to have each listener write one sentence about one of the speech's strengths and one sentence about one of its weaknesses.