I think it's all about self-esteem when it comes to talking in public; I had low self-esteem through high school, and feared when people looked at me. I always thought they were making fun of me, or were going to if they had to see my face and realize I exist.
However, it always boggled me on how that class clown, or the student that just yaps-yaps-yaps over the teacher, have half the classroom as friends, and play practical jokes in public out in the hallways could be so afraid to stand in front of the class and read the history report. I always think "Come on, man, you talk to these people all the time, you talk over these people when they are giving their speech, don't tell me you're freak'n 'shy' now!". It's strange how public speaking is such a big deal, for various reasons, some reasons not making sense at all, but everyone is different I guess.
I have to say, college was a lot easier to speak in than high school, because I was surrounded by adults, who I knew wouldn't tease me, or make fart jokes while I'm saying my speech; they were mature people, who understand how cruel it can be to harass others, so it made speaking easier for me. I have to say, I thought I was afraid to publicly speak until I went to college and talked in front of respectable adults who listened and waited their turn (even if they were bored out of their mind in their head! XD)