Oh, I don't think it necessarily needs to rely on VERBAL explanation (though I have noticed that this is really in vogue right now in K-8).
In fact, it's probably even better to be able to break apart a problem into individual, logical mathematical/computational steps that follow one another even without the use of words.
A lot of 'gestalt' mathy kids struggle with that, particularly if they themselves don't need to do the computations step-wise. But it is important. Our solution when we run up against that one is to increase the problem complexity until DD can no longer do the entire problem in her head.
