We got neuropsych testing for DS when he was just-turned 5, and looking back, I wish we'd waited a bit. We have a long neuropsych report, but it can be boiled down to comment the neuropsych made during our meeting with her, "I can't diagnose him with anything, but something's not quite right about this kid." It was really difficult for him to sustain engagement through the whole test at that age. I suspect we'd get somewhat different results if we tested him now, and different still in another year or two. So I want to wait for a bit more (also, we can't afford to test him again right now).
