The actress' debut film role came in 1999 Disney movie The Thirteenth Year and she's since gone on to make more than 20 movies, including 2008's Twilight, which shot her to worldwide stardom.
Stewart carried on her studies during the first few years of her acting career, but then dropped out to pursue movie stardom full time - relying instead on a private tutor.
The 19 year old admits she was happy to put high school behind her - because she hated it.
She says, "I was glad to leave school. I couldn't relate to kids my own age. They are mean, they don't give you a chance. I think the social aspects, I haven't missed out on. I am around people constantly. I meet hundreds of people at work. Once you have done with school, you realised it's just a smaller version of life."
But the star still remembers the bullies who made her life unbearable when they found out about her acting.
She adds, "When I was there, I was never the type of girl to be walking around talking about acting, so I didn't get a lot of hassle until someone found out. I was trying to play it down, but I definitely got, 'Oh she's such a b**ch.' They'd never spoken to me, but instantly they were like, 'You are so rude.' I am not rude."