I do not think that there is any question here -- the author is clearly challenging the ideas of race relations that were held by the majority of people in Maycomb during the time in which this book is set.
I think that the best way to see this is to look at who has what racial values. The people who are most admired within the book, the Finch family, have very progressive ideas about race. The people who are less admired have much different views. I think that this shows that Lee is trying to say "look at the Finches. Be like Atticus, don't be like Aunt Alexandra or, worse yet, Bob Ewell."
I think that one of the main points of the book is to challenge the status quo in terms of race relations.
Coming in the wake of the famous case of Brown v. the Board of Education of Topeka, Kansas, there is little doubt that Harper Lee challenges the concept of racial relations in her home state of Alabama in the 1950s. After all, the South took years before they finally integrated their public schools. And, just two years before the publication of To Kill a Mockingbird, a black teen was killed because he whistled at a white woman in a grocery store in Alabama's neighboring state, Mississippi. However, the two men accused were acquitted by the all-white jury of men much as Bob Ewell was not charged and Tom Robinson accused.
With a setting parallel to these major events, and with realistic portrayals that reflected the segregated South, such as the jury of all white males and a trial of a man who also is accused of being forward with a white woman, there is, clearly, evidence of the author, Harper Lee, issuing a challenge to those who hold to the status quo regarding race relations.
I agree with the first two answers.
I believe Harper Lee's direct challenge is issued in Atticus' closing remarks at the trial. If the entire novel is looked at as historical fiction, and Lee as simply a voice - the story teller - of attitudes that were true in small southern towns during the 1930s, then certainly she could have remained un-opinionated and even anonymous.
But Atticus' closing in the courtroom is too incriminating to be ignored.
"There is one way in this country in which all men are created equal... that institution, gentlemen, is a court... in the name of God, do your duty." (Chapter 20)
For the rest of the novel, Lee allows her readers to choose whom to empathize with... but in this speech - it is obvious what her real purpose was. She is challenging America (even in the 1960s when the book was published) to keep justice fair and equal.
Harper Lee's novel was considered highly controversial upon release in part because of her sympathetic treatment of Tom Robinson and African-Americans in general--highly unusual for the time it was written as well as for the era of the story (1930s). Some critics believe that Miss Lee did not go far enough in her support of African-American rights, but To Kill a Mockingbird was nevertheless a novel that gave an accurate portrayal of 1930s small-town Southern life. Many white Southerners refused to allow Negroes in their homes at all during this time period (even as domestic workers), so Calpurnia's portrayal as a near family member showed both Miss Lee's and Atticus's open-mindedness on the black-white issue.
Your question is quite an interesting proposition as I am doing a very similar essay for my english teacher.
one of the greatest points in the novel is when the character Julia Finch has to fight with Cecil Murphy in the schoolhouse. She did some terrible things such as ignoring Estella's beautiful store.
This is a good example of the challenge that Dickens wrote about.