So make friends with them. Next thing you know you make really good friends and do the stuff they like to do and overdose on cocaine 2 weeks later.
... Escalated quicker than I thought but you get the point!
Not allowing someone in their group is a behaviour of third graders. You probably wouldn't like being in that group anyway. Lucifer is right, (love that username btw, is there any chance you chose it after Lucifer from Supernatural? Or did you have the original Biblical version in mind?) just find someone you can relate to, even if they aren't the most popular kids in school. And if you can't find anyone, you can always try imaginary characters to spend time with, meaning you can bring a book to school and pass the time by reading.
I tried this once, and I made an anime friend, but that was at the end of the year :/ so I just sit in the corner and let people think I'm a nerd (which I'm proud to be one)
Then they're just not the droids you're looking for. That doesn't mean you'll be alone forever, it just means that you gotta search outside of school if you want to make friends. It's not your fault, nor theirs (okay maybe a bit theirs because it's rude not allow someone into your group); classes are filled randomly, which means it may occur that you won't have anything in common with any of your classmates. In that case you just gotta search somewhere else.
Geez, I dunno. Find some out of school activities, like some sport or a language course or something. I've heard dancing lessons are a decent way to meet people, though I've never attended any, so I can't tell. Or if you're really good at a certain school subject, you can start tutoring dumber and/or younger students. It's a way to meet new people and get money, which is a win-win situation! But instead of making excuses to everything I suggest, how about you think of something yourself since nothing I say is good enough for you? If you won't try, you won't succeed.
Just take a book to school with you. It'll solve your problem, widen your vocabulary, deepen your general knowledge, might even light up your imagination and motivate you to create something yourself. Books are awesome.
Really? People in your class are real douchebags, then. I take my Kindle to school and nobody says a word, because a lot of people in our class like to read as well (not sure if that makes us nice people or just extremely antisocial). In any case, maybe one of the books will give you an idea of a witty comeback you can deliver them. They have no right to laugh at you for spending time the way you do and if they do, they deserve no attention from you and you should just ignore them. That's what I did at elementary school, anyway.
... Escalated quicker than I thought but you get the point!