Oh, and sometimes I get part of the problem wrong on purpose so that he has to correct me. He likes that, too.
But arithmetic really came to him virtually all at once (except division) right around 4.5yo. Before that, he was counting, but nothing exceptional was happening that I could see. When it blossomed, it came on fast. This was helped by toys/games like Bakugon and Pokemon. The cards require adding, subtracting and/or multiplying (depending upon the game and the cards they get) to play, so he was highly motivated to figure it out. By the time he was 5yo and a couple of months, DS5 was multiplying 2 digits in his head.
This may be utterly irrelevant for your DS, of course, but it's something to think about. A lot of GT kids really like that sort of mathy game.
