Tips on how to not be shy?

So I tend to be a loud, typical person around my friends, and at home. But whenever I meet new people or talk to teachers, I get really shy and awkward and don't know what to say. So basically,

SHY

X Parents

X Friends

√ Teachers

√ New People

I get good grades, maintain a 4.0, but my teachers keep telling my parents I don't participate in class. My Social Studies teacher confronted me and told me that I shouldn't be afraid of answering questions in class, but I didn't have the guts to tell her that wasn't it. She said that I work better in small groups, but I really hate working with people in general, mostly because I like to keep my academic life and social life a little separated. Mostly I work better in small groups because the teacher isn't there and there is always a friend or two of mine in the group. Anyway, I don't raise my hand in class because I really just don't want to. I don't see why I should, the teachers know the answers anyway. And I know the answers 95% of the time.

Off the topic of teachers, and on to the topic of new people. I always get really shy when I meet new people. Kids my age. My parent's friends. Boys. Girls. Doesn't matter who. I never know what to say, and tend to try and stay away.

Anyway, thanks for listening to my problems, I could use all the tips you can give.