Students learn best about public speaking in a live setting. They need to be able to hear, speak, experience, and engage.
There are many ways to do this. From an early age, children can begin re-telling stories using expressive techniques. This helps with memorization. To increase the ability to improvise, you can have them re-tell stories with a twist. Pretend play - or simulations - is a great way to begin!
Another idea is for them to explain to you what they are doing or what they have learned, sort of like "re-teaching" back to you. Not only does this help their communication skills, but it helps you to know that they are learning and remembering.
As they get older, work on more listening strategies, persuasive speaking strategies, evaluating various messages, media influence, how to ask questions to gain the right answers, body language, etc.
Students should study and write speeches, and use peer evaluation to give each other feedback, as well as learn how to use various presentation media when giving a speech (visual aides such as drawing while talking, powerpoint presentations, holding up objects or photos, etc).
The following videos and articles are offered to PLUS members to help you teach children how to speak and be confident in their speaking: