Both stories in some ways examine the ideas of civilization and raise questions about the essence of evil and human nature and all sorts of other things. Coral Island focuses on three boys that end up on a tropical island after wrecking their ship. Unlike the boys on the island in Lord of the Flies, the three boys establish a rather idyllic lifestyle on the island and it is only after leaving the island that they begin to encounter the ugliness of human nature and some of the same evil, etc. that the boys in Lord of the Flies encounter amongst themselves.
Golding's book was in some ways a response to The Coral Island as he felt that the idealistic way that the boys were represented he showed what he felt was a more realistic interpretation where the evil was also present within the boys.