The book [Stuttering is Cool](http://www.stutteringiscool.com/stuttering-is-cool-book/) recommends saying at the beginning of a presentation that you're a person who stutters. I seem to have misplaced my copy, so I can't quote it directly, but the idea is to make it clear that you might take longer saying things and that it's because of your speech disfluency, not anything that might be at all related to the presentation itself. IIRC, one of the things that it recommends if you're uncomfortable doing that is to say it in the form of a joke, like, "The good news is, I've prepared quite a short presentation for you today. The bad news is, because of my speech impediment, that's unlikely to save very much time." That might not be an option when it's for school, but it's something to think about. Also, this might go without saying, but it's important to remember that if others have a problem with your stuttering, that's a problem with them, not with you. Never look at your stutter as a fault in your character. It's the intolerance of stuttering that's a fault in the character of others.