Just read your input. I am 39 and just got diagnosed with ADD. I can relate with your child. I was pretty good at math upto 12th grade. And I got into a great technical school. Once there, there were 3 out of 4 years of advanced math and I flunked one and came close to failing in other math tests there. Reason (now I understand), was details and inferences like you said. Even now, my math and problem solving is great but I can’t remember formulae, etc. My exam sheets used to be full of work to find the basic formulae because I couldn’t remember their details.
Another part, I am a facts guy too. Love reading wikipedia all the time but if you give me a 100-page novel or any other book, it will take 2 months for me to complete. I thought I was weak, but it was just distractions as you mentioned. My parents set no rules for me but they really couldn’t observe the issues you mentioned. For them I was doing pretty well. I have done well generally in life but I know that I suffered because of low self esteem over times. I don’t have any answers as I am seeking myself. One thing I can tell you though is that I have done and may have helped me to get through all this without medication or counseling is probably through meditation. I have meditated 5-10 mins a day since my childhood. I don’t know for sure but that may have helped.