I had a similar problem at my son's last school. My son is actually ADHD, but honestly, it doesn't matter in that type of situation. Expecting a kid to WANT to do a bunch of boring worksheets is just silly. Unless the child just enjoys writing, in and of itself, a kid is going to choose to do pretty much anything else over that.
I asked the Principal straight out "Why would he want to do that when he can just go read his book?" She had no answer, just sympathy. That's part of the reason we changed schools. Expecting young children to be okay with worksheets, and not receive any real instruction that teaches them anything is bullsh*t, IMO. We still aren't where we need to be, but at least I don't have people telling me they just can't help him because he isn't interested in doing 500 worksheets every day!