A student just assaulted me how do I file a police report?

I'm not going to go to administration with this one. A student overhead threw a heavy metal chair at my head, hitting it, and then beat me in the head with his fists. He was sent home, and I'm expected to not skip a beat. That's fine, whatever. I would like to file a police report as an eff-you to the school and an eff-you to the student. The student is 9 years old. How do I proceed? Thanks.