Perplexing Behavior

How do you calm a willful child? My children, and I know most will chalk this up to parental bragging, are extremely intelligent, caring children. What leads them to have anger issues? I understand we all need to find our ground and learn how to be assertive without infringing on the rights of others. How do I teach this? A note came home from the teacher saying she’s intelligent but rude to her co-students. I’m at a loss. . . I try to be nice - almost to a fault and I’m trying to lead by example while still instilling right & wrong in them. I guess I’ll do the easiest thing possible right now - I’ve spoken to her about it and explained that you have to treat others as you want to be treated. - now it’s time to Google it. . .