If it helps, try focusing on what you want to say instead of how you want to say it. If you "waste" all your energy on thinking how you want to say something, you might forget what you wanted to say in the first place. And I know, when you forget what you wanted to say, stuttering is inevitable (at least for me it was), you get even more stressed than before. You should practice to learn the text of presentation by heart, at least the main points. For example when you listen to someone giving a speech, do you listen to what they are saying or to how they are saying or pronouncing words? Probably you care about the thought of the speech, the meaning. Same is same for your classmates. And for those who are laughing at you, I know, it's pretty horrible but mostly those people are not happy with themselves, so their solution is to laugh at someone else's struggles so they can feel better. That's low...but it's how it is. And who are they to you anyway? Bunch of "nothing ", so starting giving them the recognition they deserve- none.