Tools of Characterization
Before we learn the boys' names, Golding uses labels as a characterization tool, such as "the fair boy," and "the fat boy." Bothered? We are, too. It just doesn't seem right for the boys to be typecast like that.
Except, it turns out that "the fat boy" isn't much different from "Piggy," and that even names like "Ralph" and "Jack" are just descriptions. (Ralph means "counsel," by the way—nifty, isn't it?) In other words, what seems "primitive" might be just a slightly skewed version of what we do in "civilized society": label things according to their appearances.
Golding makes a point of telling us what everyone looks like, even the minor characters, and he seems to expect us to draw the right conclusions from those descriptions. In Chapter One, we learn that Ralph is attractive (and therefore a natural leader); Piggy is overweight (therefore an outcast) and wears glasses (an intellectual); Jack is "tall, thin, and bony […] ugly without silliness" (possibly an embittered usurper); and Roger is "a slight, furtive boy" (shifty and lacking depth).
Golding isn't being complicated here. What you see is what you get: no one surprises us by being pretty and evil, or ugly but good—except maybe Piggy.
Speech and Dialogue
Golding's characters are kids, and they use language that children, particularly British children, would actually use—or, would have used in 1954. We're talking about things like "you can jolly well go up the mountain," "you shut up!" "wacco," and "sucks to you!" In fact, one of the things they like best about the island is that they can talk any way they want.
We don't learn much about these characters' back stories—we know that Ralph's dad is in the navy, and that Piggy lives with his aunt—so Piggy's dialect makes him stand out as working class, saying things like "them fruit" and "can't catch me breath" (1). Traditionally, England has been a very class-conscious society. Accent and dialect matter, or used to matter, much more than they do in the U.S. So, what's Golding saying by making the clever Piggy working class?