Your DS's experience in math sounds a lot like mine. When I was seven, I hated math. I used to shove my paper into my desk, incomplete. When the teacher noticed I hadn't turned in my paper, I folded my arms and told her I hadn't done it. The problem was all about calculations, which can be extraordinarily boring. It's all repetitive and procedural. For an intuitive, concept-oriented brain, there's no reward, because there's nothing new in it.

It got better later, when Algebra and Geometry happened. I have a trophy for being the most outstanding math student in my junior high, and two others for math competitions.