What is symbolism of the mailbox in Toni Cade Cambera's story, The Lesson?

The mailbox where the children meet Miss Moore before going on their daytrips symbolizes a point of departure from their neighborhood. It represents contact with the world outside, and it is a place where local items are sent out into the greater society. Just like the letters that collect in the mailbox, Miss Moore gathers the children there to begin their journey into a larger world.