Yup, and in DS's case it's not that he's more languagey than mathy! I remember noticing this at about the same point, i.e. when he was happy with multiplication and fractions but could still make errors in basic addition. We never bothered drilling addition and subtraction facts (though we didn't object when school did it a bit) trusting that they'd get automatic after he'd been using them for a while longer; e.g. you can't do long multiplication without practising digit addition! Might have done if he hadn't been choosing to spend so much time on those things though. We did encourage him to learn his times tables by rote, a little while later, using Timez Attack.
Love that Timez Attack - DS4 loves to play from the beginning each time and DS2 loves to watch. And they are both learning along the way... even though I am not sure that DS2 understands the concept of multiplication - he knows his 2 times table! haha
