Does your school have iPads? There is an adaptive math program called Front Row that DS7's teacher is using. I believe that it has a free version. It is Common Core aligned. DS likes it (DD did not), but he is blowing through multiple grade levels so I am not sure how long it will help.
In some ways, I think that reading is easier - let him choose his own "right level" books to read and perhaps look into a vocabulary/spelling curriculum like Wordly Wise or Caesar's English at the right level (I would see if the upper grades or the gifted program at your DS's school already uses one of these).
I agree about it being harder with the younger set if they need to work independently. Ideally, they would find him a tutor or form a small "right level" group for him (but this can be disappointing, because the school often doesn't grasp just how advanced some of these kiddos are). Please let us know how it goes!
