When I was in elementary and junior high, I had this happen too. Then I went to a new high school and went deep into a depressive, anxiety-ridden state. Since then, asking to read aloud causes me to stutter badly. Even being asked to read something aloud now (ten years later) causes that conditioned response to kick in, and my heart begins to pound and my mind races. It sucks because I remember being younger and being able to stand in front of a class and spout off two pages of a book like it was nothing. Now I've become conditioned to find those situations uncomfortable. It's a part of my speech that has confused and frustrated me. The only silver lining I can find was in presentations in university, I would memorize my entire presentation rather than read off a sheet because it helped me be more fluent. Also, memorizing it helped me get higher marks because I was often more prepared and articulate as a result.