Final answer:
Trevor's stepdad encouraged Trevor to fight back against the bullies as a life lesson in self-defense and standing up to challenges.
Step-by-step explanation:
When Trevor's stepdad found out that Trevor had been bullied, he encouraged Trevor to fight back. It's imperative for children to learn how to deal with challenges and stand up for themselves, and in this instance, Trevor's stepdad believed that confronting the situation personally would be a valuable lesson.