The issue isn't really speed per se, but more self-monitoring. Many children (especially those with EF dysfunctions like ADHD) don't really know what self-monitoring looks like, so they think they are checking their work when they really aren't. You might consider walking her through checking her work, including verbalizing the mental process, so that she gets a chance to see what it actually consists of. Model for her how you check your work, then have her demonstrate for you, talking her own way through it. Go through this cycle on a regular/daily basis for a couple of weeks at home. Develop a short mental checklist for reviewing one's own work. E.g., with my own children, they know that the mental checklist for math work is 1) did I answer the question? 2) does my answer make sense? 3) do I have the correct units? Of course, one could add many other items to the checklist, but I don't expect anyone to remember more than about three or four items, even after many rounds of guided practice. This is mainly to hit some of the big potential trouble spots, and also to give direction to the process of monitoring and editing one's own work. So for this example, you might have her write three checks next to each math problem, as she answers each of the question involved in checking her work. The first one means she asked question 1, the second, question 2, etc. Once she becomes reasonably fluent with this at home, have her practice doing it at school, as well. Give the teacher a heads up that you've been working on this with her at home, so that, firstly, the check marks don't get unexpectedly penalized due to misunderstanding, and secondly, so the teacher has the option of reinforcing and cueing the use of the system.
