Make a chart to record your thoughts about what the boy finds out about himself and the world in "Araby."
To identify the theme of a story, it is often helpful to focus on what the main character learns.
This question is one that requires the initiative of the student. But, to assist you in your endeavor, here are a few things to consider. You may wish to draw a a pyramid of plot as created by Gustav Freytag, a German dramatist and novelist. As you probably know, the base of this pyramid is the exposition, in which the setting and character are introduced. Then, the rising action is the line upward to the apex of the pyramid. At the apex is the climax, the point of emotional intensity--for Joyce's character it is the epiphany. On the line from the apex back to the base is the falling action and then the point of connection of the base line and the side of the pyramid is the denouement, or resolution of the plot.
Setting up this diagram, you can peruse the story and plug in the actions that are appropriate to each point. For instance, in the exposition and the rising action, as well, the boy is completely infatuated with Mangan's sister. Every morning he lies on the floor of his parlour watching her door, and "her name was like a summons to all my foolish blood." Her image joins him, he narrates.
...my body was like a harp [symbol of Ireland, by the way], and her words and gestures were like fingers running upon the wires.
There is even some foreshadowing in the boy's mention of his "innumerable follies [that] laid waste my waking and sleeping thoughts." Later, as he carries groceries through the crowd for his mother, the boy idealizes Mangan's sister as the fair maiden for whom, he, the knight, seeks the holy grail (Rising action). With the boy as the narrator, his thoughts, speech, and actions are what reveal his character to you, the reader. By charting the plot, you can place these actions or thoughts into the appropriate place so that your discussion of his realizations will be in order. Good luck!