the town's disapproval of Atticus taking on the Tom Robinson case, he never considers backing down from his obligation to defend Tom. He risks his life defending Tom from the lynch mob at the jail, and the Negroes of Maycomb love him for his determined courtroom defense of Tom, even after the jury brings back a guilty verdict. Threats are made against him by Bob Ewell afterward, but Atticus tries to calm his family's fears and hopes that all will be well instead of taking action against Bob. The father in Atticus always has time for his children, and he never changes his expectations of them from beginning to end. 

Only twice do I see faulty reasoning in Atticus' thinking. One comes when he claims that the Ku Klux Klan is no longer in existence around Maycomb. It is historically obvious that the Klan never went away during the 1930s, especially in rural Alabama. It may have been that he was only trying to ease his family's worries about the upcoming trial. Atticus also seems confused following the death of Bob Ewell when he thinks that Jem has killed Bob. It takes some serious explaining of the actual facts from Heck Tate to convince Atticus that it was actually Boo Radley who killed Bob. But aside from these two minor flaws, Atticus is the same Atticus throughout To Kill a Mockingbird.     

I don’t think Atticus changes much at all over the course of the novel. Throughout the book, he remains morally sound in his thinking and actions and he does this in every situation from the courthouse to his home. If there is any change, it is not discernible. Certainly, he is disheartened by the outcome with Tom Robinson’s trial, but he probably expected this and realized that the social evolution of Maycomb would be a much more gradual process and could not expect a town so steeped in tradition and racist thinking to change over the course of just one trial. He is, maybe, the most forthright and morally justified character in all of American literature. So, as unbelievably good as he is, that’s just the point; he represents ethical justice in totality; he doesn’t need to change.

In Harper Lee's story, To Kill a Mockingbird, Atticus doesn't change as much as the children do. He is a man of intellect with a keen sense of right and wrong. He is their moral compass.

Atticus's own actions in arguing the Robinson case demonstrate this kind of courage, and his behavior throughout embodies values of dignity, integrity, determination, and tolerance.

Atticus remains this way throughout the kids' dealings with the Radleys (when they are trying to get Boo to come out), with Mrs. Dubose and the flowers Jem destroys, and the court cast of Tom Robinson; he is even consistent at the end when he thinks Jem has killed Bob Ewell. Not even to protect Jem does he want to act a lie, or he's afraid his children will no longer respect him, and won't see the world in the same way.

'Heck,' Atticus's back was turned. 'If this thing's hushed up it'll be a simple denial to Jem of the way I've tried to raise him. Sometimes I think I'm a total failure as a parent, but I'm all they've got. Before Jem looks at anyone else he looks at me, and I've tried to live so I can look squarely back at him...if I connived at something like this, frankly I couldn't meet his eye, and the day I can't do that I'll know I've lost him. I don't want to lose him and Scout, because they're all I've got.'

Atticus thinks he is getting older quickly, and over those couple of years, it may seem that way to him: of course the kids think he is ancient.

As the children grow, they perceive Atticus differently: as when they learn he had to take Tom's case (though the man Atticus is would never have said no) and that he is a good shot with a gun. They begin to see him differently as they mature.

However, if anything changes in Atticus it would be how he is different after Tom Robinson's case. He says that every lawyer has one case that really affects him, and he figures this was the one for him.

And as for the night he almost loses the children to Bob Ewell's attack, it takes something out of him. I think he was not enough aware of the evil in men's hearts, as he never thought Ewell would come after his children instead of him. The split second when they were almost lost to him forever had to be a riveting moment for Atticus the father.

All in all, Atticus is the one constant in the book, just as a parent should be a constant in his/her child's life.

A more appropriate question is, "How does Scout's understanding of Atticus's courage change?" Atticus is not a dynamic character; he is essentially the same person at the end of the novel as he was at the beginning. But he changes the lives of others - notably Scout and Jem. As the novel progresses, our understanding of Atticus increases through Scout's narration. She learns what a deeply principled and courageous person he is, as she learns that there are different forms of courage. Can you trace Scout's growing understanding of her father?

Honestly, strictly speaking, I don't think his courage changes at all. Look at how he faced down the rabid dog, and how calm he was. He faced the courtroom, or the pack of men in the night, the same way. However, if we look at how it manifests, we can name a major difference: his courage, and his entire character, goes from latent and private to active and public. He stands up to and in some ways for his entire community, rather than keeping his soul under wraps.