Question: I'm kind of quiet and don't really like to talk much in class. I'm smart but teachers barely notice me because I get nervous and don't participate during class discussions. Is there anything I can do about this--not only for college admissions but also for my future in general?
Being an introvert is probably part of your hard-wiring, but sometimes being too quiet in class can compromise your grades and the way that your teachers regard you.
One thing you can try is to put yourself on a "training regime" very much like an approach that might be taken by someone who wants to get in better shape but hates exercise. That is, set goals for yourself. At first, keep the bar very low. For instance, you could begin by saying that you will raise your hand and volunteer once a day in just one of your classes. After the first week or two, make that once in every class ... or whatever seems to fit your needs and your schedule. (Some classes, for instance, may have little place for discussion, while in others it may be easier to volunteer more often.) Keep a written chart or record of your participation progress and reward yourself with a special treat if you meet your goals. Learning to reward yourself is a good adult survival skill anyway. As you get older, you'll find that increasingly the only rewards you get may be the ones you give yourself. So decide ahead of time what might be appropriate--whether it's the CD you've wanted to buy since September, a hot fudge sundae, a school night devoted to trashy books or TV, etc. You might also want to get your parents on board for this. If you feel comfortable doing so, tell them about your plan and your goals and ask if they will chip in with a "prize" once you reach them.
Another thing you might try is to get your teachers involved. Ask to speak with each one privately before or after class. Tell them what you've told us--that you want to improve your public-speaking comfort level. They will notice you more once you've admitted your discomfort, and they may be more apt to call on you when your hand is waving when they recognize that you're trying hard to surmount your fears.
If you haven't already done so, you can try participating occasionally in worthwhile online chats. While I personally am glad that chat boards didn't exist when I was a teenager (I wouldn't have ever gotten a thing done!), you may benefit from limited participation in useful ones, like the College Confidential discussion you'll find at http://www.collegeconfidential.com/discus/index.html . While I urge you not to fritter away too much time in Cyberspace, you may find that your confidence gets a boost when you share your thoughts anonymously with strangers, and this way you can get some useful information about the college admission process at the same time. Perhaps your online confidence will translate into classroom confidence.
Finally, this won't solve your problem but you may enjoy reading more about why you do what you do. Go to http://www.humanmetrics.com/cgi-win/JTypes2.asp and take the quick online test. Once you get your "results" you can follow the links and read more about your personality type. You will also see lists of other introverts who went on to do great things in life nonetheless.