When doing long divsion with DS11, so far the only math practice he abhors, we had an important realization. He can divide, with accuracy, faster in his head than he can writing out all the steps. So...how to convince him to do division the way the schools want him to do it?
Get him to do things like 7834095.56 / 143.8 ? Or can he really do that in his head? I'm serious; make the sums hard enough that he sees the benefit of writing it out. It's great that he has strong mental arithmetic too. Sometimes he'll have to grin and bear the requirement to write out working for something he can do confidently in his head, but if for now he needs practice, it's probably better to practise on things he can't do in his head, because that's less frustrating! (At the same time, encourage estimation and other sanity checks.)