I'm not sure how to teach addition or subtraction - it was just there with DS. But I saw him learn multiplication and division in a very visual way.
He started with Star Wars clones and arranged them in grids, all this in preparation for battles with DH. DH's was all over the place, but not so for my son. He was particular, and boy was he upset if one fell over while he was arranging! Anyway, that got too expensive so I persuaded him to try with those cheap battlepacks of soldiers. Worked like a dream! It's a very visual way of learning - he figured out how many soldiers he had depending on the length and width, and if one row or one section got wiped out, he'd figure out how many he'd had left. He also learnt to love certain numbers, 9 being one, because it was "so beautiful".
I'm not sure how to persuade a kid to arrange soldiers into grids the whole day though. In fact, DH was positive DS had Asperger traits at the time.
