The most obvious contrast in these three selections is the format. "Christmas, 1970" is a free-verse poem, "Uncle Rock" is a short story in prose form, and "We Real Cool" is a short but structured poem composed of four couplets.
There are strong similarities, however. Each once can be seen as a cultural commentary on the life of minorities in America. Castillo is Cuban-American, Gilb is half-Mexican in heritage, and Brooks is African-American.
Each of these three writers draws on their differentiated experiences in their writing. In "Christmas, 1970," Castillo implies that this is the characters' first Christmas together in America, and the children are excited to put up the tree, but their mother will just "cry into the new year/ with Lidia and Emerito/ our elderly downstairs neighbors." She seems to be weeping for what they have given up by moving.
In "Uncle Rock," Gilb shows a young Mexican-American boy named Erick, who rarely talks, but watches his mother struggle with her new life in America. She talks about the old days in Mexico, which confuses him because, from what she says about it, it sounds terrible. She wants to find a good man to marry who can help her provide a stable home for Erick. Erick observes many potential suitors pass through the story. Some are rude and behave inappropriately towards his mother, but one takes him to his first baseball game.
Brooks's "We Real Cool" is about a group of young African-American boys playing pool in Chicago. Brooks is well-known for her short pieces depicting the urban poor. She uses "we" constantly in the poem, showing how much of the boys' sense of identity comes from their group identity. The rhythm of the writing and the references within the poem to jazz are a connection to the heavy emphasis on music within Brooks's culture.
In your essay, perhaps you could emphasize the different formats of these three pieces, as well as the three different minority cultures which they represent, while discussing similarities such as figurative language and somewhat auto-biographical cultural commentary.