Youngsters typically dread giving oral presentations because it involves standing in front of the class to present their work. They eventually realize that this is just nerves, and the more often they do a presentation the easier it becomes. Children gain confidence in themselves, pride in their work and the chance to learn from what the other children did. This idea can be used for pretty much any subject.
Possibly a bit more elementary school than middle school, but this concept remains the same and can be altered as needed. Try to relate this topic to a school subject. Ask the children to bring in an item from home, and instead of just saying what it is describe how it is manufactured and suggest improvements that could be made. Also, discuss why it is useful.
By the time children get to middle school they are at a stage of personal development that allows for debates to start taking place in the classroom. This eventually leads to debate team in later grades. Obviously 11-year-olds will not debate political ideology, but it may be interesting to get them to debate topics relevant to their age group, such as the education system. This can improve their confidence and give teachers a chance to listen to their ideas.
This tactic has been used in English classes for decades and is still very effective. Instead of getting children to read quietly let them all read a few pages out loud to the class. This will encourage them to read, show who is having troubles and promote confidence in public speaking.
This may have to wait till the last years of middle school or even high school but setting up mock job or college interviews is a good way for a child to get used to that situation. This can be done individually or in groups.