How does Harper Lee contrast fragmented, dysfunctional families in chapters 1-4 of To Kill A Mockingbird?

When Scout commences her first year of school, she tries
to be the explicator of the social dynamics of Maycomb, but her teacher, Miss Caroline,
is not receptive to a child's aphorisms. 

When Miss
Caroline attempts to organize the lunch period, she asks those with lunch to put it on
top of their desks.  As she traverses the rows, inspecting the childrens' lunches, she
notices that Walter Cunningham does not have anything. Scout
narrates,

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Walter Cunningham's face told everybody in the
first grade he had hookworms.  His absence of shoes told us how he got them....If Walter
had owned any shoes he would have worn them the first day of school and then discarded
them until mid-winter. He did have on a clean shirt and neatly mended
overalls.

When asked if he
forgot his lunch, Walter sets his jaw, but finally mumbles "Yeb'm."  But, when Miss
Caroline offers him a quarter with which to buy lunch, he politely refuses it. With the
urging of a classmate, Scout attempts explanation,

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"...he's a Cunningham....The Cunninghams never
took anything that they can't pay back...they get along on what they have.  They don't
have much, but they get along on
it."

Further, Scout explains
about the Cunninghams' woes with mortgages and entailment.  They are so proud, however,
that they will accept no Public Works Program jobs offered to many who were improvised
during the Great Depression.

Polite, but proud and honest,
clean, but poor, Walter Cunningham is in stark contrast to the crude, filthy,
disrespectful, arrogant Burris Ewell, who is not just "poor," but "poor white trash." 
Fittingly, his dysfunctional family lives right by the dump whereas the Cunninghams live
in the country outside town. After lunch, Miss Caroline is appalled to find lice in the
hair of this unkempt child.  Another student assumes the role of
explicator:

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"He's one of the Ewells, ma'am,...Whole school's
full of 'em.  They come first day every year and then leave.  The truant lady gets 'em
here 'cause she threatens 'em with the sheriff, but she's give up tryin' to hold
'em....Ain't got no mother...and their paw's right
contentious."

Little Chuck
Little tries to explain, too, that Burris is very mean. When Miss Caroline threatens to
report him to the principal, Burris "slouched leisurely" to the door, cursing her until
she cries; then he leaves.  Certainly, then, the contrast between the poor, but clean
and well-mannered Walter Cunningham who has a normal, loving family and Burris Ewell,
who is but a gamin who must fend for himself with no mother and an alcoholic father who
uses the welfare checks for liquor is sharp.