We also have a daughter who rushes her work, doesn't complete work, doesn't "show her best work" (according to her teacher), etc. It's really hard as a parent to encourage effort when the assignments are so far behind her capability. Our daughter is in third grade, and lately we have been trying to work with her on the concept of "if you don't SHOW the teachers that you know something, they don't KNOW that you know it." We have also told her that it makes our job easier as her advocates to get her more challenging work if she's completing assignments and not making careless errors. I've definitely seen some improvement with this approach, combined with healthy doses of empathy and a real effort on our part to improve her school environment, including applying to a specialized program for HG students next year.