In Freak the Mighty, how does sentence length in chapters 13 and 14 impact the tone of the text? Use ACE format to answer the question—include the answer to the question, textual evidence, and explanations.

In order to analyze sentence length in certain chapters of Freak the Mighty, the young adult novel Rodman Philbrick published in 1993, we have to understand key elements of the story itself. And we must compare and contrast sentence length in chapters thirteen and fourteen with sentence length in other parts of the book.
Let's start by looking at the very first paragraph of the book:

I never had a brain until Freak came along and let me borrow his for a while, and that's the truth, the whole truth. The unvanquished truth, is how Freak would say it, and for a long time it was him who did the talking. Except I had a way of saying things with my fists and my feet even before we became Freak the Mighty, slaying dragons and fools and walking high above the world.

This passage introduces us to the two primary characters, Max (who's doing the talking) and Kevin (whom he refers to as "Freak"). As we can surmise from this text, Kevin is brilliant and Max is not. But Kevin is physically handicapped, and he must wear braces on his legs. Max, on the other hand, isn't intellectually gifted, but he's big and strong. Together, as friends, they'll help to balance out each other's deficiencies. This friendship is central to the novel.
But what about sentence length? In this first chapter, we can notice that the sentences are long. You might even describe one or two of these sentences as rambling or run-on. Max is the one speaking (he's the book's narrator), and his thoughts seem to blend into one another, stream-of-consciousness-style, as if he is thinking aloud.
Now, let's look at some examples of sentence length in chapters 13 and 14. These are the first lines of chapter 13:

It's October. Friday the thirteenth. Today is unlucky. The day starts out pretty normal. The teachers think of Freak and Max as their own little unit.

In this passage, the sentences are much shorter than the sentences we read in chapter 1. Max's ideas are more concrete and decisive; his phrases are clipped. This tone suits the dark content of chapter thirteen, in which, we'll learn, Freak has an accident at school:

Later, Freak was eating American Chop Suey, his favorite meal. Suddenly he started choking and turned blue. The teacher phoned the ambulance and they went to pick him up. Max wasn't allowed to come in, even though by this time Freak was fine again. The nurses said that he would be fine. 

Max's language here is comparatively somber, if we look at it side by side with the first chapter. It's a form of foreshadowing of the events to come.
Let's take a look at chapter 14 and an example of the sentences in it:

Max is downstairs putting gift wrap on a present when he hears yelling from upstairs. He crept up the stairs and listened at the door. His Grim wanted to carry a gun around the house, and Gram was against it. They said that Killer Cane could come at any minute now that he was up for parole. Max opened the door and asked his Grim whether he would come. Apparently the court made it so he wasn't allowed to get within a mile of the house, or he would be thrown back in jail. This is why a gun was a good idea to keep.

Here, the sentences are longer than the sentences of chapter 13 but shorter and more straightforward than the sentences of chapter 1. What can we assume about this? Max, it seems, is more "himself" in chapter 1, relaxed and unconcerned about some of the frightening or stressful things that will happen later in the book. By chapter 13, when Freak has his accident in the cafeteria, Max is worried, and he relays information in a more concise way, just delivering the facts.
By chapter 14, it seems like Max has relaxed a little bit: Freak has recovered from the accident, and he's fine. He returns, at least partly, to his free-form, stream-of-consciousness way of speaking or thinking, so we see longer sentences. But in short order, the scary prospect of his father, an ex-convict, being released from prison, and the notion that his grandfather feels like he must carry a gun around the house, is anxiety-producing. He's not relaxed here, and the clipped sentence structure reflects that.
When Max is calm, his sentences are longer and even run on sometimes. When he's feeling worried about the things going on in his life, reporting information about Freak's accident or his violent father being let out of prison, the sentences are short, journalistic, as if he's just delivering the information without reflecting much on how he feels.