The appendix includes Mr. Browne's precepts for the year. They overwhelmingly encourage students to be good friends, be kind, to immerse themselves in their community, and to be curious. It then includes "postcard precepts" from students that Mr. Browne receives over the summer. Henry's mentions not being friends with jerks, Summer's talks about not hurting people's feelings, and Julian's says that it's good to start over. August's precept is his newfound belief that everyone should get a standing ovation once in their lives.
When Julian writes that it's good to start over, it offers hope that even he will start choosing to act kindly in his new school. Further, because Julian is changing schools and will therefore be thrown into an entirely new social structure, it'll give him the opportunity to form a better, less toxic social structure, as well as make decisions uninhibited by his past poor choices at Beecher Prep.