I also have two boys and both have different personalities . Both are ADHD, one gives more problem with being to fidgety and not sitting in class but is extremely bright . The other is well behaved but is easily distracted , lose things , talks impulsively … and gets his Ds and Fs.
We have been able to get better in grades by going back to basics . He was failing in reading the deal is he can’t comprehend because he reads with no fluency and comprehension then gets lost . So back to read for him ask what he understood from very basic book like bob books he is 7 years old .Math he was having big problems to add and subtract … it results he was struggling to count . Now you may think this is because he had a bad education … not really . The way he needs to learn and process information is that he needs to do this simple work on a daily basis so he can retain it . Everyday he needs to read and write , not by just doing the work from school but by going back to basic materials. Find out what his weaknesses are and start from there .
Changing diet , exercise and vitamins also has helped my children . Hope you can find the piece to the puzzle soon . Wishing you good luck .