As with all stories and novels, there can be multiple themes playing out at one time, in one scene, or throughout the whole thing. Look at the assignment you have been given and ask yourself what the teacher expects you to do. Is your teacher asking you to decide on one of the main themes and to write a two-page paper on it? If so, you will want to come up with a theme that you can show supporting textual evidence by quote and page number.
To help you with determining some themes that you will choose, here is a list:
The legal system and how it works in the South in the 1930s
Childhood's point of view
Standing for what is right when everyone disagrees with you.
Check out the link below for further ideas on themes for To Kill a Mockingbird. Good Luck!
Fitting into society is a challenge.
Growing up is a challenge.
Social Class towards its community.
Racisim and Discrimination
Lying brings bad results