What makes Jem and Scout begin to ''part company'' in "To Kill a Mockingbird"?

In Part II of To Kill a Mockingbird,
the relationship between Jem and Scout grows more distant for the following
reasons:

• Jem is an adolescent now, nearly 13,
  and he becomes annoyed with his child sister.


• Jem is
  growing more masculine, patterning himself after Atticus.  Instead of playing the "Boo
  Radley Game," as he did with Scout in Part I, Jem wants to fire his air
  rifle.


• Jem has grown much more serious in Part II because
  of the trial.  He senses the racial injustice much more than Scout, and it bothers him.
   As a result, he grows more distant and withdrawn.


• The
  author uses separation (segregation) as a theme, building toward the end when the
  children will be attacked by Bob Ewell.