What if you've exhausted your options at your tween's school and the bullying hasn't abated?
You may want to involve local law enforcement. If your child has been threatened, it's a crime. If your child has been assaulted, it's a crime. Even if you only suspect these things have happened and your child isn't speaking up, you can ask for guidance from your School Resource Office (a partnership with local police departments that places an officer at a school part-time) or from local investigators. Keep in mind that if your child's been threatened, even if it was anonymously, school can become a scary undertaking. This makes it nearly impossible to concentrate on schoolwork, sports or anything else.
In the end, even if everyone else fails your child, you simply don't have that option. Change everything if you must. Consider a new school, or one of the many virtual schools now available, like K12.com or InsightSchools.net. It may seem drastic, but it can make all the difference in your child's attitude and their own pattern of behavior, too. And, it doesn't have to be forever. Doing something different, if only for one school year, can often take care of the problem permanently.