My DS7 in particular just has real confidence issues. He actually knows ahead of time a lot more than I expect him too, but panics immediately if he sees something in a format he hasn't seen before and shuts down. Of course, 5 minutes later he might be breezing through the same thing like he's known it forever.

I do agree about the mental math component. I think I'm not actually teaching DS anything about math. More about notation and showing his work.