My son has sort of picked his own self-calming techniques, and it was more a matter of me recognizing that this is what they were. Right now, for example. He is crossed the room, making noises, bumping in to my chair, etc. "Pacing." We used to try to stop it, given that it is destructive towards the furniture and really annoying to us. Then we experimented with allowing it. And, like magic, his moods got better.
What is harder for kids to learn is when they are headed towards a melt-down, so that they can enter into a self-calming process. If it's sensory overload, removing themselves from the situation is good. If it's just overall stress, something like pacing works.
I know that is kind of sketchy information, but I have a work deadline I need to get back to. Hopefully it helps a little.
I remembered the other night, btw, that it was at 8 or 9 that we got so worried we actually talked about medication. Instead, we found a nice group for my son to go to, and that extra bit of talking seemed to help. Sometimes kids need to hear suggestions from a person other than a parent, and the group provided that.
And, yes, it WILL get better. Keep your cool, get to the sources.
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Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).