This is what happens in real life. As we encounter challenges, new people and places, and successes, we change. We may look at the world differently once we've been to a new place, or we may learn patience or forgiveness based on a humbling encounter with another person. These life lessons are part of what makes us human, and reading about them helps us to see the world from different points of view.
Additionally, learning about static and dynamic characters can help your students to become critical thinkers. When introducing the concepts of static and dynamic characters, it can be helpful to start with a story everyone already knows. For example, you could use a movie most kids saw when they were younger, like The Incredibles.
In The Incredibles, there are lots of different characters. Some change over the course of the movie, and others don't. For example, Mr. and Mrs. Incredible change quite a lot. When the movie opens, they are young and fearless. They seem indestructible. In the middle of the movie, they are beaten down by the challenges life as dealt them, but then they learn to overcome those challenges and evolve, and in the end, they are changed once again. They are dynamic characters.
Fro-Zone and Edna Mode are good examples of static characters. They're not as important to the main action of the plot, and they don't change over the course of the story. They provide comic relief, and they show us interesting aspects of the main characters, but they don't change.
Once you have explained static and dynamic characters using a story everyone knows, you can introduce the new book you're going to read. Old Yeller is a great book for teaching about static and dynamic characters. Travis is a 14-year-old boy who is given the job of being the man of the house while his father is away herding cattle to Kansas for several months. The experiences of those months change Travis forever; he's a very likeable, relatable dynamic character.
Minor characters, like Little Arliss and Bud Searcy, are important to the action of the story, but they don't change like Travis does during the story. Interestingly, although Bud Searcy doesn't change during the story, Travis learns to see him in a different way because he has grown up and learned to understand people better. These insights make for great discussions and essay topics for your students.