The parent of the nine year old boy sounds too similar.
We have 4 children and our 5 year old son is bright and has outburst that come from left field. None of these episodes every occur at school or friends houses. His friends enjoy coming over but they only parallel play.
Dear parent of 5 year old,
The manual will be ready for publication in a couple of months. If you want, I can add your name to the list of parents who want to be notified as soon as it is published. For a younger child like yours, you would focus on part 1 of the manual, which has interventions for parents to use, while part 2 of the manual is a cognitive behavioral plan with worksheets you do with your child. Depending on how verbal your child is, you may be able to get to part 2 after putting into practice part 1.
In part 1, you start out by carefully observing the sequence of your child's outbursts to see if you can discern any patterns. Then you try to catch the outbursts in the early stage and use distraction or calming techniques that I outline in the manual. You try to plan for situations where your child is more likely to overreact, and change something in the sequence to try to head off an outburst. You cannot plan for everything as some outbursts are quick and unpredictable. You should ignore your child while he is in the midst of an outburst, as long as he is not hurting anyone or breaking anything of value, and resume talking to him after he calms down.
Another general rule is that the younger the child the more likely you will see anger overload, as younger children's brains are not as developed. But by using these strategies you will help your child's emotional and biological development, since behavioral change and brain development go hand in hand.