As an incoming senior in high school I've used this tactic since freshmen year, be open about it. After every class on the first day of school, stay behind and talk with your teacher. Say that you attend speech therapy and struggle with public speaking. Tell them that you would feel much more comfortable in the class if you could make a deal about speaking infront of the class. Suggest that you do oral presentations before or after school or even during free periods. Tell them your situation and they will understand. I've never had a problem with any of my teachers not wanting to work with me. And if they are stubborn, tell your speech pathologist at your school and they would be happy to explain to your teachers. Trust me, I'm right there with you.