I first want to commend you — you’re doing amazing things for your brother, and you’re only 17, and you struggle with ADHD yourself. You are awesome!
Now, you are right about the executive functioning deficits hampering his abilities in math. My son is gifted in math and did most of it in his head, until he hit long, multi-step problems. Now he struggles with math tremendously. He loses his place in the steps, or misses a little mistake that snowballs into a big mistake, and he’s overwhelmed before he even begins to solve a problem, because he knows it’s going to be wicked hard for him.
What helps is creating a master example with the steps broken down, in different colors, and lots of notes on it, not just an example (which is what his teachers usually send home – he’s a sophomore). There’s a reason Khan Academy uses different colors in their videos, it visually breaks up the steps at first glance.
If he’s doing something where you can make kind of a master template and make copies so he can use it over and over, that would be ideal. Going back and forth between two things is often an issue for those with executive functioning and/or working memory struggles.
ADDconnect Moderator, Author on Parenting ADHD, Mom to teen boy with ADHD, LDs, and autism