Tyro Bergen Timeline and Summary

Tyro is assigned as Bart's "Big Brother" at Baileywell. This means he's supposed to be Bart's friend and mentor but instead Tyro bullies Bart. It starts with small stuff, like pouring ketchup all over Bart's lunch, and slowly escalates to physical violence and even death threats.
After Bart vandalizes Tyro's car, Tyro and his parents are called in for a meeting at Dr. Bratton's office. Tyro apologizes to Bart for the bullying, but it comes across as insincere.
Like Bart, Tyro has to perform community service to make up for his bad behavior. He gets assigned to volunteer at a local homeless shelter.
For whatever reason, Tyro stops bullying Bart. They have lunch together one day, and Tyro's pretty friendly—or at least what passes as friendly coming from Tyro.
Tyro and his family run into Bart at the hospital. Tyro's sister is on her deathbed—and the same person Bart's befriended through his community service.
When Bart mentions Nola at school, Tyro punches him. It seems like he's returned to his old method of dealing with his problems—viva the bullying.