Oh he sounds so much like ds1!
He has been trying extra hard at school this year and desperately trying to be 'super good' for his new teacher - who he adores, then coming home and letting rip on his family.
I swear she didn't believe me, until the past couple of weeks, when he has had other stuff going on, tired, coming down with a bug, we went away for a night etc and all of a sudden he started refusing to do things at school. Poor woman looked visibly shell shocked when I went to collect him last week and she'd pretty much had a whole day of him refusing to do what she asked him.
We have exactly the same language 'worthless' and 'hopeless' and 'useless' for describing himself if he gets so much as one thing wrong and 'the worst day ever' 'disasterous' etc for any day that doesn't go 100% to plan. His feelings diary has helped him to learn that there's good and bad in any day/week/month and nothing is all bad, but unfortunately not to be so perfectionist and hard on himself.
One of his favourite phrases is "Why should I? What's the point?" then no matter how much you explain why - or what the point is - he just won't have it.
Like you, we pick our battles, but certain things are non-negotiable and he just has to do as he's told, whether he likes it or not - he doesn't like this, but he does accept it.
Ds also needs regular breaks from class, in fact both the EP and OT put it in their reports that it should be worked into his day, for physical, psychological and sensory reason. To facilitate this, he has been given the job of tidying the bookshelves in the corridor - which gives him a legitimate reason for being out of the class. He earns merit marks for doing this job as well - which boosts his self esteem. He also has a couple of regular jobs in the classroom and when he needs a break, he is able to go and do one of those - I think he has a particular bookcase he's in charge of in there, but am not sure what the other job. Teacher also tries to involve him in giving out sheets and books etc to make sure he's not just stuck at a desk for an extended length of time.
As for getting him through things he can't deal/cope with, rather than just doesn't want to do (although it's sometimes hard to know which is which) we try to break things down a bit. So for example he had a book review to do as part of a project homework, but did everything he could to avoid it, because he knew he couldn't explain how he felt about the book. The first thing we got him to do was just read the assignment brief and write a few words down that came into his head about the book. They were just a handful fact-based words - but we were able to reward him with an extra 10 mins nintendo time for complying and we left it there for that night. Next time we got him to put half of the words into sentences that answered a question on his writing frame - again 10 minutes earned and left it there. Then the same again with the other words and again a reward. Then over two night he transferred his sentences onto the actual writing frame and was rewarded each time.
I know it sounds like it was easy, but actually each step was like pulling teeth and involved lots of shouting and tears - but - he was able to be successful at each bite-sized element and ultimately at the whole assignment - which he proudly took into school today. I then let his teacher know how hard it was and she will most probably award him a merit mark for effort - so another positive reinforcement.
With the smiley face thing - could you suggest a three part system sad face, normal face and smiley face, representing not good, doing well and extra good - would that work?