In Hinton's That Was Then, This Is Now, what does Bryon learn from Mark, and how does it help him change?

Bryon learned from Mark that one's actions can negatively affect other people and that consequences are essential in teaching individuals the difference between right and wrong. At the beginning of the novel, Bryon willingly broke the law with Mark and did not feel bad about how his actions hurt others. As the novel progresses, Bryon matures and begins to feel empathy for those around him. He realizes that Mark has no conscience and does not understand the concept of right and wrong. Mark's willingness to harm others and not think twice about taking advantage of people concerns Byron. After hearing Mike's story, witnessing Charlie die, and finding M&M high off of LSD, Byron's perspective on life changes and he understands that Mark is a dangerous person. Mark's actions and disregard for others teaches Bryon that in order to make the world a better place, he must take responsibility and do everything that he can to stop those who are willing to hurt people. Although Bryon loses his best friend, he does the right thing by calling the police to lock up a criminal.