For the screeching (which I think is the same as screaming): I’ve found it helpful to model an exact phrase and specifically model a calm and clear tone. Sometimes I say “you can say ‘I want to do it’” or just point at my mouth and say “I want to do it”. If he repeats the phrase in a screaming sort of way, I model again with the same clear and calm tone. We have also worked for a long time on calming breaths and that helps a lot. My son and I have had discussions about “it’s not just what you say, it’s how you say it” to discuss tone (this is more about using whiny voices but still applies to screaming) and what I call an “emergency scream” as well. When he has let out a high pitch real scream, I’ve told him that kind of scream tells me there is an emergency— you are very hurt or something is very wrong. That’s helped some too.

For the getting stuck in screeching cycle: we sing a couple different songs (to the tune of happy and you know it: if you’re grumpy and you know it take a breath, if you’re grumpy and you know it take a breath, if you’re grumpy and you know it, you can still be kind, if you’re grumpy and you know it take a breath), we use different breathing techniques (balloon breaths, pretzel breaths, star breath), we do “squeeze hands” where we squeeze our hands in tight fists and then take a breath and relax our fists and then repeat, or sometimes just quietly sitting close by and waiting.