When we hear from parents "My kid has been bullied for weeks now" my first reaction is that I'm sorry if we knew about it we would help. When we know about a conflict between kids (99% of issues are conflict and this is the difference) we encourage them to make strong choices. If someone is mean, ask them to stop, or walk away, and get help from an adult. Too often kids jump straight from asking to stop to hitting the other kid back. This obviously creates a bigger problem.
The biggest issue we see is when a conflict begins kids "FLIP THEIR LID", which is the fight or flight response our brain does under stress. When your lid is flipped, you don't have access to the rational thinking parts of the brain, or the frontal cortex, and they will most likely make a poor choice. As a school one of our goals is around self-regulation. We teach kids how to keep their ids on. We are putting time and resources to teacher learning and student learning in this area.
Often both children in a conflict have flipped their lids and aren't thinking. We get them separated, calm, work them through better choices they will make next time, and help them apologize for their actions. The final step is to promise to let us know if it happens again, so we can follow up. Of course as incidents continue and escalate we use progressive discipline to deal with that.
As parents, you can help by using the same words as us, encouraging kids to seek help when needed so we can work together. When your child tells you, we hope you will tell us too! Together we are strong!