Many students do math very quickly. For some, a quick pace might be appropriate if they are cognitively engaged and monitoring their thinking at this speed. However, for most students, doing math too quickly means rushing through problems without fully engaging their minds, impulsively writing down answers before they have thought them through, and completing problems on autopilot without taking thought as to what they are really doing. Speedy math often leads to under-learning the material, creating sloppy and often illegible work, and of course, making preventable mistakes.
Students have different internal experiences and thoughts that can lead them to do math too quickly. I encourage you to think about your specific students and what their reasons might be. Here are some of the things that might be going on inside your students' heads and bodies:
The Skill To Build
The best way to help a struggling math student is to help them to develop skills to address their difficulties. In the case of the speedy math student, the skill we want to teach is:
Give your brain time -- it needs it to think clearly when you do math.
Or, as I say lovingly to my students once they understand the skill we are trying to build: