Toni Bambara's "Blues Ain't No Mockin' Bird" is apparently set in the South as the dialects used are reflective of this geographical area. These dialects are African American Vernacular English and Southern American English.
Ms. Bambara, who was born in Harlem in 1939, probably had ancestors (possibly parents) who were part of the Great Migration from the South, which begun in 1916. Also, Ms. Bambara lived in Georgia when she attended Spelman College in Atlanta. She would then be familiar with what is now called African American Vernacular English because she would have heard it both in Harlem and in Georgia.
The language of the Cain family of "Blues Ain't No Mockin' Bird" is a patois, now termed African American Vernacular English. The dialect of the white men, known as Southern American English, is similar to that of the Cain family except that the Cains' dialect has the added influence of the Creole language, a mixture of English and a native African tongue spoken by slaves.
Because of the strong historical ties of African Americans to the South, the dialect that developed in their English is not dissimilar from that of the poorer whites who came from the British Isles. For these men worked on the plantations as overseers and other jobs on the land; thus, they had close contact with the slaves. These lower class British people would have spoken English that was removed from the standard, unlike the plantation owners. Since the South was an area that did not have the influx of other European immigrants, much of the English grammar and vocabulary used did not change as it did elsewhere. Consequently, some archaic verb forms and words were retained. Two examples are the word yonder and the use of archaic English past participles. (e.g., the use of saw rather than seen—Have you saw him? This usage is in Romeo and Juliet: Romeo's mother asks Benvolio, "Have you saw him today?").
Without a doubt, Bambara's skillful use of these dialects enriches her story and makes the telling of the narrative more effective.