What is Lee's purpose in describing Scout's first day of school in To Kill a Mockingbird?

In addition to the response above, I think it contributes
to painting a picture of the class system in Maycomb and Scout's rejection of the status
quo, both of which will be integral parts of her understanding of the
trial.

Scout's school experience introduces us to the
Cunninghams, the Ewells, the bus children and how they compare with Scout
intellectually. Scout, far superior, still has moral values and sees how the
aforementioned gimmicks are truly a rip-off.

Scout is not
okay with the system of school, nor will she later be okay with the system of racism
when she watches it unfold in the trial.

Additionally, I
think Lee takes this school experience chapter to stab at the problems of public
education... ironically many of those same problems still exist today. We try to serve
the needs of a diversely growing group of children in a society where information grows
faster than our teachers.