A For a very angry little boy in my class I used a traffic light system. It was an A4 poster with three colour disks with instructions - red for "count to 10", amber for "slowly take three deep breaths" and green for "feeling calm? Go back to your seat". He could put his hand on each part of the poster as he did the steps. At first he needed a quiet reminder to use them but then he would get used to going by himself. The poster was tucked away in a corner of the room so other children wouldn't ask him what he was doing.
A I did a number of things that have helped with a volatile Year 3 boy. I talked to the rest of the class about the signs to watch out for when he gets angry and to stay out of his way when this happens. The rest of the class are very good at ignoring his behaviour. I would praise him when he was calm, and give a "pep talk" before playtimes - who he was going to play with, what he was going to do. I gave him a "responsible" job which made him feel important and act responsibly. It's important to try and get the parents onside - make sure the strategies are followed through at home. He is now making huge progress behaviour-wise and also academically.
A On an anger management course, I learned that it takes a junior school child on average 40 minutes to calm down from an anger episode, while an adult takes about an hour. Consequently there is often a further clash as the adult often has not fully calmed down, followed by guilt and depression afterwards if it is handled badly. Talk it through, separate the behaviour from the child, and when bringing them back into the classroom, be positive. It was compared to a firework - you need to prolong the fuse or dampen down the spark.