Your teacher wants you to think about where and when The Lord of the Flies occurs (that is the setting) and then explain how this setting contributes to the narrative (the narrative is the story).
The kids are stranded on an apparently tropical island in what amounts to the middle of nowhere. The author doesn’t want the reader to focus too much on the specific location, so he doesn’t offer clues that would lead you to that information. We know that it’s hot, it rains, there is jungle terrain, wild animals etc.—all things you would expect to encounter on a tropical island.
The island is wild. There are no other living people. This fact about the setting forces the boys to have to construct their own society. This is the real crux of Golding’s story. Look at the society that these boys create. Since they are left to their own devices, they splinter into warring factions, develop superstitions, and begin to worship strange things. None of this would have been possible in a more conventional setting, because the kids have to be separated from the civilizing force of adult discipline and expectation.
The setting then enables Golding to explore the idea that humanity is not far removed from its very primitive, and frequently evil, roots.
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