When I was in the ninth grade, almost all of my friends were reading Lord of the Flies in English class as their first reading selection. Not my class; we were reading A Separate Peace. At the end of the year, my teacher confessed that we didn't read Lord of the Flies because a) she hated it; and b) she believes that starting with the most boring novel in the world is a good way to let her students know that her class will not be a walk in the park. She was my favorite teacher for a reason.
After a plane crashes on an uninhabited island, a group of young boys must figure out how to survive without the adult supervision to which they are accustomed. There is an initial attempt to maintain order: electing a chief, establishing conduct rules for meetings, and organizing themselves into hunters and builders. Eventually the structure breaks down as the boys' primitive nature begins to emerge. Their remote existence encourages power struggles, bullying, and deadly violence.
It wasn't exactly my cup of tea, but I can understand and appreciate it's significance. The symbolic presence of democracy (the conch and their meetings), the metamorphosis from a civilized to natural state, and the contrast of rational thought versus irrational instincts are all concepts that are explored thoroughly in this tale of survival (and make great essay topics). The power struggles are foreshadowed almost immediately, which can make for some tense reading when you just know something horrible is about to happen. The allegorical characters and their actions elicit both sympathy and apathy from the reader, which makes for a rapid emotional changes as the reader moves along with the story.
Because the YA world is overrun by dystopias, I would align Lord of the Flies with Michael Grant's Gone series due to their similar themes. In Gone, everyone over the age of 15 disappears simultaneously, leaving the children to fend for themselves. Naturally, there are power struggles and violence as the children try to figure out what is happening. While the series falls more into the sci-fi/supernatural genres, the adventure, survival, and power structure elements are great parallels to the high school English class standard that is Lord of the Flies.