On page 10-11, Jefferey notices Lindsey having trouble with her books in the hallway. Knowing that she is the new girl, Jefferey offers to help her. This is when the two meet. This is a big part in the story because the two play a huge part in the story later on.
Don't worry. I'll help you!
Oh no! I dropped my books!
On page 28-29, Jefferey finds that the mail has come in. As he takes the mail, he realizes that there is a letter from his school. He quickly regrets opening the letter, because it is about the test he has to take to see if he can get to the next grade. This is important because it started a big part in the book, whether or not Jefferey will be passing.
On page 145, Jefferey realizes that Lindsey has a mistletoe in her room. This doesn't seem like much, but really, it gives us a big hint of what happens later on in the story.