You are beating your head against the wall. If it were an issue of the official reading curriculum, then the focus tends to be on writing and you are unlikely to get "differentiation" (other than the built-in open-endedness of many writing assignments) unless the school approved subject acceleration. If it were an issue of "free reading," then send your DS' own books (purchases or public library loans) to school and inform (not ask) the school that is what your DS will be reading. In DS/DD's classrooms over the years, many kids often brought in their own books as well as used what was avaiable in the 100 book challenge baskets or on the teacher's book shelves. As for the "resources" provided to be used at home, just don't use it and provide your own. For example, our school provides lots of electronic resources like Study Island and First in Math, etc. Unfortunately, these tend to be way too basic as well as with Study Island ending in 5th grade and First in Math ending in 8th grade (at least for elementary kids) so that my DS outgrew Study Island in 2nd grade and First in Math in 3rd grade. The resources available online and at the public library are tremendous. Save your fight for the crucial issues such as subject acceleration for your DS.
