In addition to those already cited, here are some other examples of the motif of Appearances vs. Reality:

• Scout's perception of the group of men who congregate in the front yard of the Finch home.  She states that there are only two reasons that men do this gathering before a house.  But, neither of these reasons is why they come this particular night.
• Scout and Jem's perception of their neighbor is false:  Mrs. Dubose's vituperative comments about Atticus do not stem from her hatred of the man because, as Jem later learns, she is under the influence of the drug morphine.
• The children's trip to Calpurnia's church turns out differently from what they expect.  As they dress, Jem remarks, "It's like we're going to Mardi Gras."  However, they find the church to be poorly furnished and without prayer books as in their own church.  Yet, it is filled with better Christians than the white church which houses many a sanctimonious hypocrite such as those at Aunt Alexandra's tea. 

Here are a few more obscure answers (if you want to be the kid that finds the ones no one else has said):

- On the first day of school Miss Caroline assumes by Walter's appearance that he needs money for lunch, will take it, and is able to pay her back.  She does not realize how insulting her charity actually is - even though the rest of the class does.

- Scout then insults Miss Caroline by attempting to be diplomatic.  Miss Caroline again reads into Scout's attitude as disrespectful and out of line.  Really, Scout has only innocent intentions.  Ironically, Scout feels sorry for Miss Caroline.

- Mr. Dophus Raymond always drinks out of a bottle hidden by a paper bag - perhaps wanting to give the appearance that he is "the town drunk" (a way to escape judgement for his 'mixed children') but it turns out he's just drinking Coke.

In To Kill a Mockingbird, Harper Lee uses situational irony to address the theme of "appearance versus reality."  Here are some examples:

• Aunt Alexandra's Missionary Tea Party appears to be a philanthropic organization but, in reality, it is a social group who refuses to help those in its own community.
• The lynch mob outside the jail wants revenge against Tom, but after Scout disarms Mr. Cunningham, the mob feels guilty and ashamed for its actions.
• The all white jury is expected to deliver a unanimously guilty verdict against Tom, but it takes longer than expected because Mr. Cunningham tries to convince them otherwise.
• The fire of Miss Maudie's house appears to be a personal disaster for her, but, in reality, it gives her more opportunities to garden outside.