In Chapter Two of To Kill a Mockingbird, Scout gets in trouble with Miss Caroline for explaining why Walter does not have a lunch and why he could not possibly repay Miss Caroline if she was to lend him a quarter to buy one: he is a Cunningham and too poor. Rather than handle this situation sensitively, Miss Caroline grabs Scout by the collar, hauls her back to her desk, hits her hand with a ruler, then makes her stand in a corner.
In Chapter Three, Scout gets revenge for her public humiliation by catching Walter in the schoolyard and rubbing his nose in the dirt. Seeing this, Jem invites Walter to dinner at the Finches' house, where Atticus makes the boy feel welcome. Atticus and Walter discuss the crops and problems on the farm, a conversation which neither Jem nor Scout can keep up with. When Walter requests some molasses to eat on his vegetables and meat, Atticus happily provides him with some and makes sure that Scout is silenced when she begins to protest over this perceived breach of civility.
Despite their differences in upbringing and etiquette, Atticus clearly is capable of respecting Walter's country ways, while Miss Caroline only makes him feel like an outcast.
During chapter 3, Walter went home with Jem and Scout for lunch. While eating around the talble, Atticus asked Walter questions about farming and his family. This demonstrated respect and care for Walter regardless of class or social standing. Atticus talked to Walter like he would talk to an adult or friend. He treated Walter no different than his own children. Finally, as Walter had an interest to have some syrup, Atticus made sure he could have some. As Scout showed great disgust at Walter putting the syrup on his ham, Atticus had no problem with it. Walter seemed to feel very at home with Atticus.