My DS (8 years old) goes to an "academically rigorous" school. The guideline for his homework is that it should take 15 minutes of undivided and focused work to finish the math part - parents are told to write a note so that the teacher knows if it is too much and they will work with the child to rectify any issues. They also ask the parents to write a note if they think that the child is doing busy work as homework. He gets 2-3 pages of math - 80% of the time, he finishes in 10 minutes (word problems), but on some days, he works for 30-35 minutes to get it done - and those are for difficult challenge problems which are not straight forward application of concepts.
So, I think that 1 hour on 1 subject at this grade level is too much (whether for a child who is slowing down due to writing challenges or for a tired child at the end of a long day). Since you feel that it is a lot of busywork, I suggest that you use the spec-ed teacher's help to either reduce the math homework load to 20% of the current load (= 20 minutes) or ask for the parent to be able to choose which part of the packet your DS should spend time on or just skip math homework on alternate days.
In addition to losing his love for math, too much time on 1 subject leads to reduced time for other homework, test prep and projects in other subjects and even less time for after school sports and such things. Definitely take up the spec-ed teacher's help to lobby for changes for your son.
