Trying to find a book

hi /book/! Back around 2000 or maybe earlier, our english class at school were group-reading a story. I'm now trying to identify what that book was, and was wondering if anyone here would be able to help me out.

From what I can remember, it had a dystopian/cyberpunk theme (less "cyber" than "punk" though.) The story primarily focused around two young characters and their plight to be together - a girl and a boy, both living in a Big Brother-style metropolis. The girl lived and grew up fairly comfortably in the suburbs, while the boy (slightly older?) lived in the slums of the city. The inner-city was separated from the suburbs by a large fence around the perimeter, which was monitored at all times, and only authorised personel could travel freely across the divide.

at some point in the story either the girl or boy sneaks across the border by holding on to the underside of a garbage truck.

unfortunately that's all i can remmeber of the story :( other than the possibility that it might be classified as a children's novel. any help?

also i hope i'm not breaking any rules. couldn't find any for this board.