Wear what ever you want to wear. Jeans and a t-shirt is fine along with hoddies. Although, I would suggest NOT wearing pajama pants. You still want your professors to take you seriously. Also, this is the time to begin buying more "adult" or "professional" clothes when you can. It will make it easier when you get an internship and enter the real world.
Hope this helps :)

Look I think jeans and a t-shirt is good , you can wear any thing which is comfortable , but take my advice ;) every couple of weeks you can wear some kind of hot skirt and high heels just to make different looks :)

Who cares? Wear what you want! Be your self! Maybe wear more girlie type t-shirts? Throw on an occasional scarf or belt for accessory. Or shoes. Don't just wear tennis shoes. Where cute ones! Maybe wear styles from Forever 21 or Urban Outfitters. But don't ever conform to something just because it'll make you popular! Find what you like!

Honestly, I wear just about anything I feel. I know people who wear nothing but pjs to their classes but I also know people who do strut around in heels. It just depends on what makes you comfortable. I personally just throw on what I think looks good and is comfortable to me. On days when I'm ridiculously tired and don't feel like trying, I'll roll out in some sweats, but most of the time I'm in jeans and a T-shirt. But when the weather permits it's fun to dress up. Why? Because it's there and I want to wear i and I'm awake enough to bother putting forth the effort. Just do what makes you happy in fashion right now.

I would say it depends on your style and what kind of reaction you're looking for. I am a vintage loving girly girl. I've noticed that I get treated not only better by my professor because I'm dressed more professionally, but also by men. Guys will almost always get the door or help you pick something up if you're dressed like a lady. They'll also talk differently around you and to you, because the realize you have higher standards for those around you.

I would say dress professionally. You don't have to wear suits or blazers to school, but dress like you care about your appearance. Teachers will notice and remember you better, and fonder when writing you letters of recomendation or for internships.

You start writing your own letter of recomendation the first day you arrive on campus. Your actions wil show them what kind of person you are.

Keep that in mind.