Some years ago, a student asked for a time-out because he was very angry and needed to cool down. I won't go into the exact circumstances, but prior to the lesson there was some dispute with a classmate and he was still reeling from the after-effects.
There was another teacher in the class, so I followed him outside to make sure he was ok. The boy was clearly trying very hard to come to terms with the anger raging inside him.
I told him that when I was a secondary school student, I also experienced rage issues.
I shared with him a simple method to manage his anger: Breath slowly. Breath deeply. Breathe gently. 1-in breath, 2 -out breath, 3-in breath, 4-out breath. Odd is inhalation and Even is exhalation.
To my surprise, the boy diligently followed my instructions and he visibly calmed down. "I feel much better." He said. I asked him to do ten more. He complied and soon was ready to go back into the classroom.
I hope I can remember to take my own advice!