The kids are not warmly recieved at the church at all. Lula goes out of her way in making her displeasure known. Calpurnia stands up for the kids and Lula backs off a bit. The kids also learn that that many in the church can't read so they came up with their own way in learning the hymns: lining. During this chapter, Cal changes her manner of speech. Of course, Scout asks why she does this and learns that Cal does this to fit in.
They felt that they were not at all accepted by the blacks and can be seen through Lula's confrontation with Calpurnia at First Purchase, designed to show that prejudice is not restricted to the whites. but is endemic in Maycomb and the southern community as well.
But they do learn something as well. During the church service, it shows them true Christianity working in a practical way, doing good to the body and the soul. The worship is true to the heart and it is uncomplicated and the sermon, while sticking to the original text, is practical in usage as the Reverend names names and is concerned not for the whole congregation but to each people individually.
They also learned something from Calpurnia, that she was forced to compromise in order to survive in the black and white societies that she lived in and despite the fact that she could speak and read English really well, she diverts back to Negro dialect when she is with the black community so that they don't think she is
"puttin' on airs to beat Moses"
This shows us that they had learn a lot of valuable lessons that they would cherished in their life for a lifetime and give them a broader insight into other people lives.
The children are not warmly accepted at the church, so they see how discrimination feels from the other side. They learn how bad that feels.