In To Kill a Mockingbird Why does Scout begin the novel as an adult then switch to a child's perspective?

In the begging of the novel is the conclusion to the end of the novel. Its telling you what happens in the end of the novel and you have to read on to figure it out but since so many years have gone by when she starts out as a child's perspective and learns more on 'how to be a lady' you can tell that she has grown up and the same with Jem