So I will start with a brief introduction of the problem.
I'm 17...

I've been with this class for like 8 months, never speaked much with girls at all, but lately things have changed, my mind aswell, and got to talk with most of them, but this one which I think she likes me is kinda strange, I don't want to take fast conclusion because I don't really know but here's the story why I think this...

First, she started to be very kind to me which is very rare from her, than yesterday she was expelled from an exam for trying to copy, and in that day like 11PM, I saw her on the MSN and asked if she was better about the exam thing, we got talking for like 1 hour or so, nothing very fancy, just normal talk...
Today, I got like 20-30 minutes late to class and teacher had change the classroom to another and without me asking to anyone this girl texts me with the classroom number, and I was like, maybe I'm right, she likes me, a person would only miss someone if she likes it or is special friend or something like that...

Now we've seen each other all day long in classes and shit but didn't talk with each other, nothing, I didn't even re-text her saying thanks or something...
Do you think I should text her or talk on MSN saying something like "Hey, I guess I forget to say thanks for saying me the classroom number..." Or any other thing?

Thanks in advance...

No, don't text her back or MSN her. You want her to chase you. You don't want to be that kid that she can always talk to when she's bored. She's DEFINITELY into you. If I were you I would just talk to her sometimes in class, be sure to be confident and make eye contact. And if you're feeling her ask her out to coffee or something. Just DON'T be that guy that is always hitting her up via text or MSN, you'll look desperate.

Try to put it in perspective so that you don't get over-excited. Remember that other girls will like you (plenty of them), and it's possible that nothing at all will come of this. Try not to place too much expectation on some specific thing happening. Just have fun, be an attractive person (as in, build an attractive lifestyle), and don't worry about it. She already likes you, so you have even less to worry about. Get rid of that fear that if you act to aloof, she'll stop liking you. It actually couldn't be further from the truth. You don't want to act aloof forever, eventually you need to open up to her, but for now just focus on you. Do what you do normally, and as long as you are being an attractive person, she will follow. Be friendly but try to shed your expectations. Things will happen when they happen, and they're not going to happen soon if you dwell on them or over-think things. In fact, quite the contrary. It's better to just have fun with the situation and not put too much empasis on it. Remember to keep living your life, and remember to hold tight to your boundries. If you have some commitment or activity that you do regularly, don't start flaking out on it in order to spend time with her. You are more important than she is. She may be cute, she may have qualities you like, but let's face it - there's probably several things about her that you're going to end up not liking and it's not likely that you're going to get married. You need to focus more on yourself at this pivotal point in your life, or you'll end up regretting throwing away your precious time on some stupid girl. Be the best you that you can, and she will follow. If not her, there will be others.

Thanks both for the answers, very appreciated, really cleared my mind!

Yes I know I should not raise my expectations neither get over-excited, I know that, I can control that. I just didn't knew what to do, that's why I decided to ask, better than doing a shit move, I guess..

The best thing I can tell you to do is be yourself. That's who she likes, right? It seems so simple but too many guys change who they are and try to be who they think she wants you to be. Not only are they almost always wrong, it's just not attractive. She's looking for a man, not a bad she-clone. So really, keep doing what you do.

Make sure your body language and your eye contact conveys how you feel, and don't be ashamed to be a little sexual about it. Look for opportunities to touch her. Have fun with it and I'm sure you'll find plenty of opportunities to tickle her, chase her around, play fight, or just touching each other while you're talking. If you're having fun, she likes you, you like her, and there's a lot of touching... everything after that will happen very, very naturally. It's the human mating dance and one you get it rolling, you'll know your part quite clearly. The worst thing you can do is over-think it. It's all very instinctual and primal, and over-thinking kills the fun of it anyways.

But try to free yourself from worrying about what's going to happen. You need to understand that if it doesn't work out, then it will work out with someone else. If you can truly remove ourself from that fear and self-doubt, you will be very, very attractive to her (and many other women). When you worry about things, your anxiety shows through in everything you do. Whatever you have to do, you've got to get it out of your mind.

Thanks once again for the inspiring word.

I'm trying to be that kinda of person, is just I need time and experience to be that person...I hope in some few years things are like I want