yelling etc for a long time in carm down

Firstly I want to thankyou for the help and training you've given, it has made a big difference to our home and family in a positive more consistent way. I feel like I can be a much better example of Christ since having had TSG training. We have an 8yr old who from a young age has had a lot of difficulty getting calm about things. For example he will often howl, bellow, thump and make a really big deal about things often in calm down places even. We have gone to him earning a chore for every time he yells, bellows very loud or thumps really loud inside or in calm down session, if he continues for sometime we have moved to him earning a major maintenance for every 5 chores or if he starts getting really fowl or abusive in his language or kicks somebody etc, basically to get some accountability or cause and affect for his actions during his out of instructional control . We normally have a 3 stage calm down system/spot which basically starts inside and the last is outside on the mat if it gets really extreme. Once he eventually gets okay, calm, accepts and takes responsibility for what ever the thing, it will move on. He is very capable and intelligent in most ways but yet seems to have quite a lot of challenging issues. For example we have been doing a distant learning program for him from the school were some of his siblings are schooling. About 2-3 weeks ago he was doing some schoolwork at home and he lost it on about the 3rd question and went out of instructional control he got up to about 290 choirs and 49 major maintenances some of which he had already earnt. (He seems to do have some trouble doing schoolwork for very long without wanting or needing to have a break especially if he's got something else on his mind like catch birds, making something etc. ) He has a boys night that he has already made some plains for which he knows he can have when he's completed his Major maintenances and choirs which as of this date are still not complete not because he doesn't do them, he's probably done well over 2 or 3 times that amount of major maintenances and choirs by now, its because he keeps earning them. He's been down at 7 major maintenances to go and gone back over 30, currently at about 10. We have tried a lot of different methods over the years to help him with some of his extreme behaviors trying to put the big focus on the positive behaviors, also acknowledging time as we have 9 kids, oldest being 11 and number 10 on the way.