The impossible situation was that the school had no evidence of bullying but they did have evidence of the girl fighting back. This kind of asymmetric situation interacts poorly with zero-tolerance policies that many schools have.
The school did not even tried. They just assumed the girl lied. When they found out the bullying was true and that girl tried to report it ... they still expelled the girl and let boys be.
The school had better options available.
I will go out and say that the school simply played out traditional believes. First, punishing victim to striking back or defending himself/herself is easier, victim should not make noise. And second, boys matter more, it is normal boyhood for them to bully girls who are reaching above their station if they defend themselves.
The first belief is non gendered, applies to any victim.
