Here is a way for students to report bullying while remaining anonymous. On a small slip, they fill out who was bullied, who was there, when and where it happened, etc.
Here you are getting a template of bullying slips that you can copy off and use all year long. I thumbtack a stack of them on my wall, and students can drop by during recess, lunch, or after school to fill one out and drop it in my teacher box. Great, non-threatening way to maintain a safe learning environment.