Explain the definition of theme to the children, so they know what it is they have to identify. A theme is an idea or message about society, life or human nature. A good example of a theme is Man against Nature, which can be found in "Moby-Dick" by Herman Melville. The book questions whether humanity has greater worth than other animal species to explore the theme of Man versus Nature and to make the reader question whether it is Captain Ahab or the whale who is the monster.
Look at the title of the book you're analyzing, and the titles of any chapters or sections it may have, then get the children to think whether these titles infer anything about the theme of the piece. For instance, the main theme of James Fenimore Cooper's "The Last of the Mohicans" is Man versus Man, shown in the ultimate destruction of the Mohican tribe. If Cooper had just wanted to refer to the person who would be the last member of the Mohican tribe, he could have called the book "Uncas." But, his use of the word "last" is poignant and infers that the end of the tribe is something to be lamented, which helps you decipher the theme of the book.
Ask your students to look at symbols and motifs in the piece of literature they're analyzing and see if these give any clues about the theme. For example, one of the themes in "Of Mice and Men" by John Steinbeck is the pursuit of the American Dream. A recurring motif in the book is George and Lennie talking about having their own ranch, which is a microcosm of the American Dream, as they believe that they can gain personal success by hard work. However, the ending of the book suggests that Steinbeck may have believed that the American Dream was dead, or at least unattainable for migrant workers and those on the lower rungs of society.
Get the children to study the dialogue and action of the story for any instances of subtext -- anything that is implied but not spoken or spelled out in the narration of the book. Subtext is often one of the keys to unlocking the theme. Shakespeare's "Hamlet" is full of subtext. One of the main themes of the play is the uncertainty of death, and what lies after it. Hamlet is uncertain whether he has seen the ghost of his father, or if he really is going mad. This is revealed subtextually by Hamlet's lack of action. He intends to kill Claudius, but keeps putting it off, as he's still uncertain on death and the afterlife.
Examine the needs and wants of the characters with your pupils. Think about emotional desires, or things they want to change, rather than just material wants. If there's something meaningful that a character wants, it might relate to the theme of the story. For example, in the Harry Potter books, Harry's biggest desire is to stop Voldemort, who is intent on destroying the non-Wizarding world and any Wizards not pure of blood. This reflects the theme of the book, which is Man versus Man.
Ask the children to try and relate the journey of the main character in the piece to their own experiences. It can help them to determine the book's theme if they learn to empathize with the protagonist, and see things from his perspective. For instance, if students can empathize with Holden Caulfield from J.D. Salinger's "The Catcher in the Rye" they will be more able to understand the major theme of otherness or alienation.