You can't judge a book by its cover, eh? Well in When You Reach Me, what a person is reading tells us quite a bit about that person. Miranda, for example, is always reading A Wrinkle in Time. Marcus has read the book too, though when Miranda meets him in the dentist's office he's reading a math book called Concepts in Mathematics. It's not color-coded like the rest of the math books kids use. Rather, "Marcus's book was different – thick, with a hard cover and small type" (14.30). This gives us a hint that maybe, just maybe, Marcus isn't like all the other kids.
Bonus round: Who else reads A Wrinkle in Time in this novel – and what does it tell us about their characters?