Bullying
Remember that phrase about bullies being the ones who need the most patience and attention? Crash is that kind of bully. He deals with a lot of anxieties and insecurities, and his method for coping is to resist change. Consequently he doesn't like new or strange things. When Penn moves in next door to the Coogans, he quickly learns that Crash is the kind of kid who doesn't adapt well to new environments. Penn finds himself the victim of Crash's bullying for over seven years before they finally get on the same page. That entire time Crash is trying to tear down Penn by mocking him in order to avoid accepting Penn for his weirdness. Crash seems to believe that he needs to make himself important, probably because he has a low self value. He accomplishes this by seeking popularity in school by joining the football team and by making fun of any kids like Penn who are on the social fringe. In the end Crash just has to learn that everyone is valuable and that fearing change won't prevent it.
Approval
At 6-years-old Crash and Penn are both at the developmental stage which asks the question of approval. Am I a good thing? Is it ok to be me? They each approach this question from different perspectives which has a strong impact on the course of their young adolescent lives. For Crash the question of approval is one of merit. He believes that he needs to earn respect and approval, especially from his peers, so he tries to become popular in school. He sets great stock in the number of friends he has, and one of his primary defense mechanisms for insecurity is bullying. Rather than feel like the weakest kid on the block, he feels compelled to prove that he's better than other people, as if trying to prove it to himself. While Crash makes some friends through this process, he ends up feeling very much alone because he hasn't really been sincere in his relationships. In the end he finds that his grandfather's approval is what he really wants. He trusts Scooter immensely, so he wants to know that his grandpa thinks highly of him. In Penn's case, he struggles with isolation and loneliness. He doesn't have the outlet of family companionship like Crash, so he really values his family. He determines early on that the can which his great-grandfather gave him full of dirt from the Missouri River is his prized possession. This means that Penn values the approval of his elders. Consequently he adapts to speak easily with adults and to spend his time learning information which may prove interesting in adult conversation. He seeks approval by trying to understand the world around him. This leads him to become a very inquisitive and relatively balanced kid all things considered.
Sacrifice
Crash and Penn are complimentary characters in this story. Their character arcs head in opposite directions, but they both inevitably demand sacrifice for the sake of improvement. Firstly, Crash has to learn to pay attention to the importance of people around him. He doesn't feel valued because he doesn't do a good job of valuing others, so that's his lesson. After Scooter's stroke, Crash notices something positive about Penn. Penn sacrifices his most prized possession -- the tin from his great-grandpa -- in order to make the old man feel better. While Penn loves that tin because of its symbolic connection to his great-grandpa's approval of him, he understands that such a noble sacrifice will be inspiring to Scooter. He sincerely gives something of himself up for the old man. Crash sees this and realizes that he hasn't been giving Penn enough credit all these years. He too finally understands that sacrifice produces character which is universally respected. In an effort to reward Penn's selflessness, Crash allows him to win the running event at school when Penn's great-grandfather is visiting. Crash understands how important the race is to Penn's great-grandfather and consequently to him, so he sacrifices his love of competition in order to give his friend a win.
