What does Scout mean when she says, “It was then, I suppose, that Jem and I first began to part company?” (p. 56) What could Lee’s purpose be for having Scout say this?

As Jem reaches his puberty years, he begins to broaden his horizons. Much of what he used to do with his little sister does not interest him anymore. Jem has more concern about living up to his father's expectations than playing childish games with Scout. This is the point where Scout realizes that the two now think differently.