Complaining to a child about what he or she has to learn OR discrediting the method by which he or she has to learn will not do the child any favors. Particularly if the child already has a learning challenge.
I would suggest that you learn the new method so you can assist the child without negativity. That doesn't mean that you can't try different methods along the way to make it easier. For now, the grades are based on lattice - not how "we used to do it."