Document everything.

Keep accurate notes and records.  The process of documentation for bullying incidents is a parental responsibility that only ends when your child is no longer in your home.  You must keep meticulous records, just as if you are the attorney representing your child.  Ask you child to do the same.  If you want to make it a fun exercise - grab a long handled spoon and pronounce on your child, "I now dub you a special junior attorney."  Empower your child.  Who knows, they may even become an attorney some day, or find a profession that utilizes such skills. 

Conduct an interview with your child and then write down a synopsis in bullet points.  If there were witnesses to the bullying, get their statements and get signatures on those statements in front of an adult if they are a minor.  Do not forget to add dates, names, times and all the who, what, when, where and why information you can find.  Write down any comments made by administrators or teachers.  These written notes may not seem like much at the time, but later, they may be a deciding point for justice in your child's favor.  These records may aid in procedural changes that could dramatically reduce bullying in your school, and of your child.

Here is an example:
"In our case, I got the information from Jared, as well as some witnesses, but I didn't write all of it down.  Consequently, I had to remember many of the details later, during interrogations and depositions.  However, there was one comment by a Vice-Principal that I did write down, which came in handy later.  When I asked the VP if he allows violent children to wander his halls stalking prey, particularly the bully who beat Jared up, he replied, "He's not that bad now, you should have seen him before he came to the middle school."  That comment told me that this bully had a record of bullying other children, and the school knew it. That was valuable information.  I was also able to do a lot more investigating because of that one comment."