Atticus tells his children to whom he has given air rifles,
"Shoot all the bluejays you want, if you can hit'em, but remember it's a sin to kill a mockingbird."
Since the mockingbird does not both gardens, or nest in corn cribs, says Miss Maudie to the children, it is wrong to harm them when all they do is "sing their hearts out for us." Thus, the mockingbird comes to be a metaphor for anyone who is harmless. Boo Radley and Tom Robinson are included in the mockingbird motif which is closely related to the Guilt and Innocence theme of Harper Lee's novel.
So, in an examination of "the mockingbird motif," you will want to look at how people form prejudices [they "kill" the mockingbirds] against both Boo and Tom when they are simple men who are innocent of any evil intent. And, in an extension of this, you will wish to examine how prejudices are formed without knowing people's knowing the facts. See the site below about themes, especially Guilt and Innocence.
***Also, there is a sample outline for your question at the second site listed.