For little children:
Use a stoplight. Red is where you’re so angry that you’re screaming and yelling and you feel like hitting someone. Yellow is where you’re upset, but you can keep calm. Green is where you aren’t upset.
You give them examples of bad stuff that could happen, things that the child encounters in a normal day. Some examples to get you thinking: The school lunch is one you don’t like. Someone breaks the Lego sculpture that you worked really hard to make. You have to wait in a line to go down the slide. A bully punches you in the stomach. You fall and scrape your knee and it hurts a lot. The teacher tells you that, because there’s an assembly, art class will be first today, instead of math.
You have the child sort what kind of thing goes in “red,” what goes in “yellow,” and what goes in “green.” It’s normal for an autistic child to put a whole bunch of things in red, a few in green, and none in yellow.
You talk about whether some of the things in “red” might fit better in yellow, and why. Hopefully, the child is willing to move a few things into “yellow.”
Then you ask the child to think about this the next time something bad happens. They need to ask themselves, “Is my feeling inside a red, or a yellow, or a green?” Then they need to ask themselves whether that temperature matches what the bad thing was.
It’s unlikely that the child will remember this instantly the next time there’s about to be a meltdown. But if you keep asking the child, “Is this a red, a yellow, or a green?” the child starts to think about checking how upset they are, and comparing it to the thing that just happened. It can help the child start learning how to pause before flying into a rage, and can get them on the path of being able to learn to how to calm themselves down.
For older kids:
Use a thermometer. The top is boiling over with anger, the bottom is complete calm. Have the kid help you come up with negative situations they encounter on a daily basis. Then the kid rates what the right level of being upset might be reasonable for each thing.
Again, it’s normal for an autistic kid to put lots of things at each extreme, especially at the raging mad end, and not many in the middle.
Go through the same process, talking about which situations might need to be moved down a level or two. (There might also be ones that ought to be moved up to a higher level– sometimes autistic kids are the target of some pretty mean things, and they don’t realize that they ought to be yelling and reporting it to an adult.) But let the kid have the ultimate decision. They need to own what the appropriate reaction ought to be.
Then point out that when something bad happens, you need to stop. When you stop, you check to see how upset you are– you check your emotional temperature. If you’re really upset, you take in a slow breath while counting to four, and you let it out even slower, while counting to seven. Then you decide whether the thing that happened deserves to have a response of you being so upset.
This is a skill that the kid develops over time, and with repeated reminders. But a firm, “Suzy, you rated what just happened at about a five, but you’re acting like it’s a nine,” can be helpful.