Yes, I have the same problem. I also have a hard time concentrating in a classroom setting, due to all the distractions, and the fact that I'm trying to take notes and keep up with what everyone is saying. I also never know when it's ok to speak, and what subject is ok to talk about at a certain point in the conversation.
Sometimes, I will inform the teacher that I have a hard time participating in class (I'm in a psychology class right now and our teacher told us to tell her that, otherwise, she'd just assume we weren't paying attention). It's a bit easier for me in a smaller group setting, where I can ask questions at a slower pace, with fewer people to worry about.