What are some examples of situational irony in Part 1 of To Kill A Mockingbird by Harper Lee?

There are two examples of situational irony in part 1 of To Kill a Mockingbird. The first is Scout's teacher's reaction when she realizes the extent of Scout's education. The second is Atticus's ability to shoot a rabid dog.

Situational irony occurs when there is a major difference between what a reader expects and what actually happens. It is usually based on a contradiction between expectation and reality.

Miss Caroline is a teacher at Scout's school. She asks Scout to read the alphabet and then asks her to read through a series of texts. When Scout is able to, Miss Caroline is not pleased. Scout says, "she discovered that I was literate and looked at me with more than faint distaste. Miss Caroline told me to tell my father not to teach me any more, it would interfere with my reading." Scout argues that her father didn't teach her; Miss Caroline refuses to believe her and repeats the order.

This is situational irony because a reader would expect a teacher to celebrate a pupil's ability to read well. Instead, Scout's teacher is unhappy that she is able to read and instructs her to try to learn less at home. She says that Atticus, Scout's father, doesn't know how to teach.

Another example of situational irony occurs in chapter 10, which opens with Scout explaining how feeble her father is. She says that he is old at nearly 50, never interested in playing football, and wears glasses because he is almost blind in his left eye. This sets up the idea that Atticus is not capable of physical pursuits.

Scout goes on to say that Atticus wouldn't teach Jem or Scout to shoot, leaving it to their Uncle Jack. So it is a surprise when Atticus is the one to shoot Tim Johnson, a local dog who went rabid. Heck is preparing to shoot and at the last second insists that Atticus take the shot. He does, and he kills the dog with one shot. Scout and Jem later find out that Atticus used to be nicknamed Ol' One-Shot for his marksmanship skills. 

This is situational irony because Atticus is set up to look like a physically weak person with bad eyesight and no experience with guns. In reality, however, he chooses not to shoot and is still excellent with a firearm after not shooting one for thirty years.