Thank you all. I sort of knew what to expect when I asked the question, but just wanted to see what others in my position had done.
DS does not have ADHD but his EF was low at around age 5, but has improved by leaps and bounds in the last year.
LAF and Mr and Mrs P: we used a math program where the rescue of a character in distress depended on timed math facts and there was absolute meltdown, distress and anxiety because of being very sensitive and being timed. So, we did a lot of very old fashioned drilling using paper and pencil. I am happy to report that math anxiety is gone - he can finish most tests (he is grade accelerated) ahead of his class mates. So, the automaticity helped a lot - we did multiplication and division facts before we started seeing improvement of speed.
puffin: in literature tests he is given a passage from the book they had read and discussed all week long (e.g. Winnie the Pooh) and then asked "why do you think that Pooh said xyz in the passage above"? I think that these questions are not too advanced. But, as you say, he might be overthinking because he is a perfectionist.
