Dandy, does your DS do maths competitions? For my DS, these raise the stakes in the right way to encourage carefulness.
I've raised the topic a few times, but he's not been interested. He holds math merely as a tool to use in other pursuits.
Another heart-to-heart last night clarified his understanding of just how much math he will face in non-math courses and that his weakness will be felt in all those areas.
So far, he's on board with the idea of re-doing incorrect problems each night with me. We reminisced about his first major math challenge, which was 3-digit long-division. That dragon was slain by working carefully through a couple problems every night for 2-3 weeks.
We also looked at the various universities that interest him, noting the SAT score ranges of accepted students. He has big dreams and I think the importance of math in reaching those goals is slowly sinking in.
