Symbolism, Imagery, Allegory
Since time and time travel are important themes in When You Reach Me, we end up seeing plenty of images of watches and clocks. Time becomes three-dimensional. It's everywhere in the novel. There's Mom's egg timer (2.1), the giant invisible clock in the sky that Marcus sees (10.5-6), Julia's little silver watch that she flings and breaks (28.14-17), and the watch Sal gets for Christmas (40.1), just to name a few. Clocks and watches are a way to measure, or make sense, of time, so the images of all those clocks and watches give us a hint that that's just what the novel is trying to do.