This isn't really an answer to your question, but it's a great resource: Emily Bazelon wrote a great book on the subject called Sticks and Stones. It's smart, thoughtful, and tries to define bullying as something that requires both a power imbalance between parties and repetition. Bazelon also argues that you need consistent voices from adults stating that real bullying isn't normal, isn't acceptable, and can often have long lasting consequences for everyone involved. A great read.