The most evident way we can see discrimination against blacks in To Kill a Mockingbird is in the trial of Tom Robinson. He is clearly an innocent man, but he does not stand a chance to be acquitted. This is because the people of Maycomb are racists, and they do not even know it.
When Scout asks Atticus if they are going to win the trial, Atticus says that they won't. Atticus knows from the beginning that he does not stand a chance, because he knows the racism that lives in Maycomb. In a conversation with his brother Atticus speaks telling words.
Why reasonable people go stark raving mad when anything involving a Negro comes up, is something I don’t pretend to understand... I just hope that Jem and Scout come to me for their answers instead of listening to the town. I hope they trust me enough... Jean Louise?”
We also see discrimination in Jem and Scout's visit to the black church. The members of the church are poor and have little. This shows that the blacks of Maycomb are marginalized. Most cannot read, and they barely scrounge up enough money to help Tom Robinson's family. In short, they are poor and powerless. When we compare this with the whites in Maycomb, such as the women's missionary society, we can see the stark difference.