Character Analysis
Robbie Turner is the son of the Tallis family's cleaning lady. On the one hand, this isn't very important at all. On the other hand, it's the single most important thing about him, and it's also his undoing.
Why It's Not Important That His Mom Is The Cleaning Lady
Robbie is lower class. His mother cleans the Tallises' house and makes money on the side by telling fortunes. His dad, Ernest, left when Robbie was little and nobody really knows where he went off to.
But so what? The class you are born into doesn't have to define you (though it definitely has an impact), and it certainly doesn't define Robbie. One of the first things we learn about him is that "He was without social unease" (1.8.16), which basically means he's way less socially awkward than we are despite being in an under-privileged position. Jack Tallis—a.k.a. Big Papa Tallis—paid for Robbie's education, and Robbie earned first-class honors. In other words, not only is Robbie well-educated, but he's smart too. We're constantly hearing about his books and reading (he compares his desperate love to that of Malvolio in Shakespeare's play Twelfth Night for example) (1.8.8), and his plans to attend medical school with Jack Tallis's support. Robbie mixes easily with his boyhood friend Leon Tallis and Leon's massively rich friend Paul Marshall, despite coming from much different beginnings from them. And, of course, he falls in love with Cecilia—and she falls in love with him—despite their vastly different social standings.
Even after Robbie is accused of rape and disgraced, his social class continues to seem largely irrelevant. While in prison, where his letters are heavily censored, he communicates his continuing passion and love to Cecilia by referencing great literary lovers. When he goes off to join the British Expeditionary Force in France during World War II, his ability to read a map and his intelligence earn him respect, even though he is a private without officer rank. The two corporals, Mace and Nettle, who he leads across France, call him "guv'nor" as a way "to settle the difficult matter of rank" (2.5). In other words, they think highly of Robbie even though nobody's making them. That's some real respect for you. Robbie's ability to speak French (learned while he was at Cambridge) proves invaluable to the three men as they trek across the French countryside.
We can see that throughout the novel it isn't Robbie's background that defines him, but his intelligence and his love—attributes which have no social class.
Why It Does Maybe Matter After All
But while Robbie's intelligence and love don't come from his social class, the contexts in which they are cultivated and flourish are. For instance, Robbie may be generally without social anxiety, but his comfort with the various members of the Tallis family is also the result of having been allowed to befriend the family. When we learn that "He had spent his childhood moving freely between the bungalow and the main house" (1.8.16), we know it wasn't his mother making that allowance nearly so much as it was Jack Tallis. Jack Tallis also pays for his education, thereby giving Robbie a better shot at realizing his intellectual potential than he likely otherwise would have had.
Robbie's courtship with Cecilia is complicated by the class gap between them. When, in an excess of confusion and shyness, he takes his shoes off to come in the house, Cecilia decides that he is "playacting the cleaning lady's son come to the big house on an errand" (1.2.43). Their odd relationship—almost siblings, and yet with a gap between them—is part of why it's hard for Robbie to tell Cecilia he's in love with her, and part of why it's hard for Cecilia to figure out she's in love with him. "That they were old friends who shared a childhood" is a "barrier" (1.11.63) even when they finally come together—though it adds to their love too.
Robbie's background has more permanent consequences as well. The reason the Tallises were so willing to believe he had raped Lola is in part, it seems, because of his class. Cecilia writes to him in prison that "I'm beginning to understand the snobbery that lay behind [the family's] stupidity," and adds that her mother "never forgave" his success at Cambridge (2.91). Grace, Robbie's mother, never doubts him; she runs after the police car that takes him away shouting, "Liars! Liars!" (1.13.48)—but Jack and Leon and Emily, who have known Robbie since he was a boy, are willing to believe the worst about him. Even though he lived almost as their brother and their son, they never, Cecilia suggests, forgot his poverty.
Not That One, Either
Interestingly, class matters not just to the Tallises, but to Robbie and Cecilia as well. The two of them are convinced that the rapist was the hired hand Danny Hardman, whose father, they think, lied to give him an alibi. After Robbie returns from France, they're both shocked to learn from Briony that the real culprit is millionaire Paul Marshall.
Once he's recovered, Robbie muses, "I suppose we owe an apology to Able Seaman Hardman" (3.458). This comes only a couple of paragraphs before Briony apologizes to Robbie and Cecilia for ruining their lives. Robbie and Cecilia, it's clear, would have ruined Danny Hardman's lives if they could—and over similar prejudices as the Tallises held about Robbie.
Class is one way people think about each other, both in the world and in Atonement. Robbie isn't just his class, but class is one of the story threads he's in. Turns out that just like in the real world, class is a pretty hard story to get out of in Atonement.
Robbie's Timeline