The story Everyone gets mad sometimes was created to help children on the autism spectrum work on their social skills, but could be useful for all children. This story explains certain warning signs that you're getting angry and the importance of using calming strategies (eg., breathing, taking a break, counting).
To help students better understand, I've added illustrations. All of the characters have been hand drawn by myself. I've also included "calming strategy" cards that can be laminated and used in the classroom.