Chewing gum helped me through High School and College. The bans on gum in K-12th grade horrify me because I would have never made it without it.

As for public speaking goes, practice in front of a mirror. I found that helped to lower my stutter problems. I also found that if I could sit during giving a presentation I was much less likely to fall, freak out, forget what I was saying, paralyze, stutter...

If you participate once per class time then that is usually more than enough to get the "participated in class" vibe with a Professor. Just try to think about areas where something is confusing you and then ask a question about it.

Are you sitting in the prime location of your classes for you? I have found that I have a specific area of any given class that is optimal to my learning due to visual and auditory problems. Usually about 6 seats in any given class. If I don't get one of those seats my learning is impaired.

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I have a Masters in Computer Engineering, so I have spent more than my fair share in classes.