What is the form of An American Childhood?

The form of An American Childhood--loose chronology, looping vignettes, microscopic observation--matches its content. Dillard's focus on skin, topography, treasure seeking, and division mirrors the way she designs her own text.
For instance, in second section, Dillard describes the local topography of Penn Avenue:

"You walked on sidewalks whose topography was as intricate as Pittsburgh's, and as hilly. Frost-heaved peaks of cement arose, broke, and over years, subsided again like Appalachians beside deep pits in which clean grass grew from what looked like black grease. Every long once in a while, someone repaired the sidewalk, to the tune of four or five squares' worth. The sidewalk was like greater Pittsburgh in this, too--cut into so many parts, so many legal divisions, that no one was responsible for all of it, and it all crumbled."

Here, Dillard zooms in on the sidewalk. Pittsburgh itself becomes the subject of her beloved microscope, its sidewalks echoing the topography she outlines in the opening pages. The sidewalk is "cut" and divided into "squares."
Shortly after describing the sidewalk, Dillard observes the streetcar, whose overhead wires "cut the sky into rectangles inside which you could compose various views as you walked." The street, too, is cut, split into cobblestones, themselves relics of the old riverbed. These small slices of the world--the squares of sky, sidewalk, or street--are the spaces of knowledge and awareness.
The structure of Dillard's narrative echoes this theme. Each vignette is itself a square, both figuratively and narrative. Through careful observation and digging at each of these small places, Dillard suggests that we can come to know and understand our world and create something, just as others "cut Mount Rushmore into faces; they chipped here and there for years."
This is Dillard's writing life. "You hacked away at the landscape and made something, or you did not do anything, and just died."