One of the main issues "The Garden Party" explores is the differences between the social classes. Laura, the main character, and her family, the Sheridans, represent the upper class. The family of the man who died, who live down the hill from the Sheridans, represents the lower class, as does the workman who comes to set up the marquee for the party. Mansfield depicts the differences between the classes with dialogue, especially slang; with numerous symbols; and with Laura's reactions.
In the beginning of the story, Laura is instructing a workman about where to place the marquee. He tells her
"you want to put it somewhere it'll give you a bang slap in the eye, if you follow me."
His use of such slang gives Laura pause. When she visits the home of the dead man, the woman there says,
"You'd like a look at 'im, wouldn't you? ... Don't be afraid, my lass. ... 'e looks a picture."
This lower class dialect shows how distinct the family is from Laura's. Laura's brother uses upper class modern slang, saying things like, "you might just give a squiz at my coat," "ra-ther," "dash off to the telephone, old girl," "what an absolutely topping hat," and "isn't it, darling?"
The story is replete with symbols of the upper class lifestyle of the Sheridans: the party itself, the marquee, the band, the arum lilies, the fancy sandwiches, and Laura's hat. These are all things that are way beyond the reach of the people who live at the bottom of the hill, the hill itself also representing the social class distinction. In contrast, the poor family's home is marked by a "wretched little kitchen, lighted by a smoky lamp."
Finally, Laura's attitude toward the different social classes shows that she is aware of the wide gap between herself and her neighbors. She seems embarrassed when talking to the workman, wondering what he is thinking about their ostentatious party. She wants her family to cancel the party in deference to the bereaved family, but her mother and siblings find that ludicrous. As the story progresses, Laura regains her comfort with her social class, basking in the praise she receives and the delight of the event. At the end, she is more impressed by death, something experienced equally by all classes, than she is by her thoughts of the social hierarchy.