I usually took a pencil or piece of chalk with myself when I had to speak in class. I played with it and it helped me to relax. Also I didn't start answering immediately and took time to adjust my posture and relax somehow. I wasn't a 100% cure but it used to give me some confidence. Also during different periods of time I felt that my fluency improves if a) I'm sitting (or leaning on something (blackboard or table) b) I'm not leaning on anything but move my hands a lot. It seems to be opposite situations but it both helped me on many occasions.