I'd say ask other school staff to see what you can do. It's completely unfair and out of your control. I have mentioned my stutter to teachers before, and they were always considerate enough to give me leeway. For example, there was a timed oral presentation I had to do and the teacher specifically said if you go over time, then you lose a bunch of points. Even though I went over time he let me keep my points. I implore you to speak to other staff members for their opinion. Someone mentioned a guidance counselor, which is not a bad idea.