Talk with school officials at the schools in your community and find out if they keep a log of violence that has occurred in the school. In some cases the log may not be available to the public, but they can give you statistics or instances and also tell your what is being done in regards to instances of violence on campus in general.
Review the school's guidebook on policies for school violence. This will keep you informed and should your child have an instance of violence, or should you hear from a fellow parent or child of an instance, you can ensure the school handles it accordingly.
Hold a meeting with parents from the school to discuss school violence. This can be a great way to hear others' concerns and hear about any instances of violence they may have experienced or heard about within the school. Should parents notice any recurring problems you can also draft a plan or proposal to the school for how they should fix these issues.
Discuss with your children what they see at school with regards to bullying and violence and instruct other parents to do the same. School violence or bullying isn't always seen by faculty and administrators, but your child might tell you as they feel safer in their home environment. If there are any issues that have been unreported make sure to report them to the school immediately. This can be done anonymously.
Talk to your local police department and ask to see any records of violent instances in schools in your area. Any instances where police were involved will be documented by police and usually crimes where police are involved are public domain. You can also voice any concerns to police over violence you have seen or found to be prevalent in schools.